Christoph Schnurr

The effect of computer navigation on blood loss and transfusion rate in TKA.

The blood loss that accompanies total knee arthroplasty (TKA) can be substantial. Many patients need perioperative blood transfusions. To avoid anemia and transfusion-related complications, the amount of blood loss and need for blood transfusions must be reduced. If standard jig instruments are used, an opening of the femoral medullary canal is required. This operative step has been recognized as a reason for elevated blood loss; it is not required if computer navigation is used. Hence, the purpose of this study was to investigate the effect of computer navigation on blood loss and transfusion rate in TKA. The data of 500 consecutive patients undergoing TKA were analyzed, and patient- and operation-related data and blood loss and transfusion rates were recorded. The total blood loss was calculated by use of the Orthopedic Surgery Transfusion Hemoglobin European Overview (OSTHEO) formula. The average blood loss in the drainages (standard procedures, 880 mL; navigated procedures, 761 mL; P=.001) and the calculated total blood loss (standard procedures, 1375 mL; navigated procedures, 1242 mL; P=.036) were significantly reduced in the navigation group. The transfusion rate of navigated procedures was almost halved (standard procedures, 0.23 transfusions/patient; navigated procedures, 0.12 transfusions/patient; P=.035). Our study demonstrated a reduced blood loss if TKAs were implanted by use of computer navigation. The diminished blood loss resulted in a 50% reduction of allogenic blood transfusions. Hence, computer navigation may be attractive for patients with a high risk of transfusions or uncommon blood groups. Prospective studies are required to verify this potential benefit of computer navigation.

Imageless navigation of hip resurfacing arthroplasty increases the implant accuracy.

Surface arthroplasty of the hip is increasingly popular. Optimising the position of the femoral component is essential to avoid early implant failures such as femoral neck fractures. Sixty hip surface replacements were retrospectively analysed. In 30 patients imageless navigation was used, and 30 patients were operated upon using conventional jigs. Accuracy, implant position, operating time, and complications have been recorded. The navigation device improved the implant position with high accuracy. Implant-shaft angles <130° and uncovered cancellous bone of the superior femoral neck could be safely avoided. After a significant learning curve, navigation took 15 minutes longer than conventional implantation. No complications were found in either group. Computer-assisted navigation allowed accurate implantation of the femoral component avoiding pitfalls of hip surface replacement. From our point of view the optimal placement of the femoral component outweighs the disadvantage of a longer operating time.RésuméLe resurfaçage de la hanche devient de plus en plus populaire. L’optimisation de la position du composant fémoral est importante afin d’éviter les échecs tels que les fractures du col. Matériel et méthode : 60 resurfaçages de hanche ont été analysés de façon rétrospective chez 30 patients en utilisant la même technique avec navigation, sans image et en comparant cette série à une série de 30 patients opérés de façon conventionnelle. La sécurité, la position de l’implant, le temps opératoire et les complications ont été rapportés. Résultats : le système de navigation améliore la position de l’implant de façon significative. Après la courbe d’apprentissage le temps de la navigation augmente de 15 minutes le temps opératoire. Aucune complication n’a été relevée dans les deux groupes. Conclusions : La technique chirurgicale assistée par la navigation permet une meilleure implantation du composant fémoral et évite les erreurs en cas de resurfaçage de hanche. Pour nous, l’amélioration de la position du composant fémoral contrebalance de façon avantageuse l’augmentation du temps opératoire.

Treatment delay of bone tumours, compilation of a sociodemographic risk profile: A retrospective study

BackgroundBone tumours are comparatively rare tumours and delays in diagnosis and treatment are common. The purpose of this study was to analyse sociodemographic risk factors for bone tumour patients in order to identify those at risk of prolonged patients delay (time span from first symptoms to consultation), professional delay (from consultation to treatment) or symptom interval (from first symptoms to treatment). Understanding these relationships might enable us to shorten time to diagnosis and therapy.MethodsWe carried out a retrospective analysis of 265 patients with bone tumours documenting sociodemographic factors, patient delay, professional delay and symptom interval. A multivariate explorative Cox model was performed for each delay.ResultsFemale gender was associated with a prolonged patient delay. Age under 30 years and rural living predisposes to a prolonged professional delay and symptom interval.ConclusionEarly diagnosis and prompt treatment are required for successful management of most bone tumour patients. We succeeded in identifying the histology independent risk factors of age under 30 years and rural habitation for treatment delay in bone tumour patients. Knowing about the existence of these risk groups age under 30 years and female gender could help the physician to diagnose bone tumours earlier. The causes for the treatment delays of patients living in a rural area have to be investigated further. If the delay initiates in the lower education of rural general physicians, further training about bone tumours might advance early detection. Hence the outcome of patients with bone tumours could be improved.

Displays mounted on cutting blocks reduce the learning curve in navigated total knee arthroplasty

The use of computer navigation in total knee arthroplasty (TKA) improves the implant alignment but increases the operation time. Studies have shown that the operation time is further prolonged due to the surgeons learning curve, and longer operation times have been associated with higher morbidity risks. It has been our hypothesis that an improvement in the human-machine interface might reduce the time required during the learning curve. Accordingly, we asked whether the use of navigation devices with a display fixed on the surgical instruments would reduce the operation time in navigated TKAs performed by navigation beginners. Thirty medical students were randomized and used two navigation devices in rotation: these were the Kolibri® device with an external display and the Dash® device with a display that was fixed on the cutting blocks. The time for adjustment of the tibial and femoral cutting blocks on knee models while using these devices was measured. A significant time reduction was demonstration when the Dash® device was used: The time reduction was 21% for the tibial block (p = 0.007), 40% for the femoral block (p < 0.001), and 32% for the whole procedure (p < 0.001). The integrated display, fixed on surgical instruments in a manner similar to a spirit level, seems to be more user-friendly for navigation beginners. Hence, unproductive time losses during the learning curve may be diminished.

Bildfreie Computernavigation von Hüftoberflächenersatzprothesen

OBJECTIVE Precise implantation of hip resurfacing arthroplasty by imageless computer navigation. Hence a malalignment of the femoral component, leading to early loss of the implant, can safely be avoided. INDICATIONS Coxarthrosis in patients with normal bone mineral density; only minor deformity of the femoral head that enables milling around the femoral neck without notching. CONTRAINDICATIONS Osteoporosis; large necrosis of the femoral head; metal allergy; small acetabular seat and corresponding wide femoral neck, leading to needless acetabular bone loss; pregnancy, lactation. SURGICAL TECHNIQUE Hip joint exposure by a standard surgical approach, bicortical placement of a Schanz screw for the navigation array in the lesser trochanter. Referencing of the epicondyles, the four planes around the femoral neck and head by use of the navigation pointer. Planning of the desired implant position on the touchscreen of the navigation device; a guide wire is inserted into the femoral head and neck using the navigated drill guide; navigated depth drilling is performed. The femoral head is milled using the standard instruments. The acetabular bone stock is prepared with the conventional instrumentation; high-viscosity cement is finger-packed on the reamed head and the femoral component is inserted. Hammer blows should be avoided to prevent microfractures. Verification of the implant position by the navigation device; displacement of the Schanz screw; joint reposition and closure of the wound. POSTOPERATIVE MANAGEMENT Standard postoperative management after hip arthroplasty. RESULTS The comparison of 40 navigated and 32 conventionally implanted ASR prostheses resulted in a significant reduction of outliers by use of computer navigation (navigated procedures: one outlier, conventional procedure: nine outliers; p<0.001). Accuracy of the navigation device was tested by analysis of planned and verified implant position: CCD angle accuracy was 1 degrees , antetorsion accuracy was 1 degrees , and offset accuracy was 1.5 mm. An ongoing computed tomography-based anatomic study proved a varus-valgus accuracy of the navigation device of 1 degrees .ZusammenfassungOperationszielPräzise Implantation von Oberflächenersatzprothesen der Hüfte durch bildfreie Computernavigation. Vermeidung von Fehlimplantationen am Femurkopf, die ein frühes Implantatversagen bedingen könnten.IndikationenKoxarthrose bei normaler Knochendichte; geringe Deformität des Hüftkopfes, so dass ein Überfräsen des Schenkelhalses ohne dessen Verletzung möglich ist.KontraindikationenOsteoporose; ausgeprägte Hüftkopfnekrose; Nickelallergie; kleine Pfanne bei breitem Schenkelhals, so dass ein unnötiger azetabulärer Knochenverlust entstehen würde; aktuelle oder geplante Schwangerschaft, Stillzeit.OperationstechnikÜber einen dorsalen Standardzugang Darstellung des Hüftgelenks, bikortikales Einbringen einer Schanz-Schraube zur Aufnahme des Referenzsterns auf Höhe des Trochanter minor. Referenzieren der Epikondylen, aller vier Ebenen des Schenkelhalses und des Hüftkopfes mit Navigationspointer; Planung der Implantatposition am steril bezogenen Bildschirm; navigiertes Einbohren eines Führungsdrahts, navigierte Tiefenfräsung. Kanüliertes Überfräsen des Hüftkopfes. Konventionelle Implantation der Pfanne; anschließend Zementieren der Femurkomponente mit hochviskösem Zement unter Vermeidung von Hammerschlägen. Verifikation der Implantatposition durch das Navigationssystem; Entfernung der Schanz-Schraube, Gelenkreposition und Wundverschluss in üblicher Weise.WeiterbehandlungMobilisation an zwei Unterarmgehstützen mit 20 kg Teilbelastung für 2 Wochen, Belastung mit halbem Körpergewicht bis zur 6. Woche, anschließend Vollbelastung und Freigabe.ErgebnisseDer Vergleich von 40 navigierten und 32 konventionell implantierten ASR®-Prothesen ergab eine signifikante Reduktion von Ausreißern durch die Computernavigation (navigiert: ein Ausreißer, konventionell: neun Ausreißer; p < 0,001). Zwischen geplanter und verifizierter, navigierter Implantatposition wurden eine Abweichung des CCD-Winkels von 1° sowie eine Differenz der Antetorsion von 1° und des Offsets von 1,5 mm gemessen. Eine weiterführende computertomographiebasierte anatomische Studie konnte eine Genauigkeit des Navigationssystems in der Frontalebene von 1° nachweisen.AbstractObjectivePrecise implantation of hip resurfacing arthroplasty by imageless computer navigation. Hence a malalignment of the femoral component, leading to early loss of the implant, can safely be avoided.IndicationsCoxarthrosis in patients with normal bone mineral density; only minor deformity of the femoral head that enables milling around the femoral neck without notching.ContraindicationsOsteoporosis; large necrosis of the femoral head; metal allergy; small acetabular seat and corresponding wide femoral neck, leading to needless acetabular bone loss; pregnancy, lactation.Surgical TechniqueHip joint exposure by a standard surgical approach, bicortical placement of a Schanz screw for the navigation array in the lesser trochanter. Referencing of the epicondyles, the four planes around the femoral neck and head by use of the navigation pointer. Planning of the desired implant position on the touchscreen of the navigation device; a guide wire is inserted into the femoral head and neck using the navigated drill guide; navigated depth drilling is performed. The femoral head is milled using the standard instruments. The acetabular bone stock is prepared with the conventional instrumentation; high-viscosity cement is finger-packed on the reamed head and the femoral component is inserted. Hammer blows should be avoided to prevent microfractures. Verification of the implant position by the navigation device; displacement of the Schanz screw; joint reposition and closure of the wound.Postoperative ManagementStandard postoperative management after hip arthroplasty.ResultsThe comparison of 40 navigated and 32 conventionally implanted ASR® prostheses resulted in a significant reduction of outliers by use of computer navigation (navigated procedures: one outlier, conventional procedure: nine outliers; p < 0.001). Accuracy of the navigation device was tested by analysis of planned and verified implant position: CCD angle accuracy was 1°, antetorsion accuracy was 1°, and offset accuracy was 1.5 mm. An ongoing computed tomography- based anatomic study proved a varus-valgus accuracy of the navigation device of 1°.

Imageless computer navigation of hip resurfacing arthroplasty

OBJECTIVE Precise implantation of hip resurfacing arthroplasty by imageless computer navigation. Hence a malalignment of the femoral component, leading to early loss of the implant, can safely be avoided. INDICATIONS Coxarthrosis in patients with normal bone mineral density; only minor deformity of the femoral head that enables milling around the femoral neck without notching. CONTRAINDICATIONS Osteoporosis; large necrosis of the femoral head; metal allergy; small acetabular seat and corresponding wide femoral neck, leading to needless acetabular bone loss; pregnancy, lactation. SURGICAL TECHNIQUE Hip joint exposure by a standard surgical approach, bicortical placement of a Schanz screw for the navigation array in the lesser trochanter. Referencing of the epicondyles, the four planes around the femoral neck and head by use of the navigation pointer. Planning of the desired implant position on the touchscreen of the navigation device; a guide wire is inserted into the femoral head and neck using the navigated drill guide; navigated depth drilling is performed. The femoral head is milled using the standard instruments. The acetabular bone stock is prepared with the conventional instrumentation; high-viscosity cement is finger-packed on the reamed head and the femoral component is inserted. Hammer blows should be avoided to prevent microfractures. Verification of the implant position by the navigation device; displacement of the Schanz screw; joint reposition and closure of the wound. POSTOPERATIVE MANAGEMENT Standard postoperative management after hip arthroplasty. RESULTS The comparison of 40 navigated and 32 conventionally implanted ASR prostheses resulted in a significant reduction of outliers by use of computer navigation (navigated procedures: one outlier, conventional procedure: nine outliers; p<0.001). Accuracy of the navigation device was tested by analysis of planned and verified implant position: CCD angle accuracy was 1 degrees , antetorsion accuracy was 1 degrees , and offset accuracy was 1.5 mm. An ongoing computed tomography-based anatomic study proved a varus-valgus accuracy of the navigation device of 1 degrees .ZusammenfassungOperationszielPräzise Implantation von Oberflächenersatzprothesen der Hüfte durch bildfreie Computernavigation. Vermeidung von Fehlimplantationen am Femurkopf, die ein frühes Implantatversagen bedingen könnten.IndikationenKoxarthrose bei normaler Knochendichte; geringe Deformität des Hüftkopfes, so dass ein Überfräsen des Schenkelhalses ohne dessen Verletzung möglich ist.KontraindikationenOsteoporose; ausgeprägte Hüftkopfnekrose; Nickelallergie; kleine Pfanne bei breitem Schenkelhals, so dass ein unnötiger azetabulärer Knochenverlust entstehen würde; aktuelle oder geplante Schwangerschaft, Stillzeit.OperationstechnikÜber einen dorsalen Standardzugang Darstellung des Hüftgelenks, bikortikales Einbringen einer Schanz-Schraube zur Aufnahme des Referenzsterns auf Höhe des Trochanter minor. Referenzieren der Epikondylen, aller vier Ebenen des Schenkelhalses und des Hüftkopfes mit Navigationspointer; Planung der Implantatposition am steril bezogenen Bildschirm; navigiertes Einbohren eines Führungsdrahts, navigierte Tiefenfräsung. Kanüliertes Überfräsen des Hüftkopfes. Konventionelle Implantation der Pfanne; anschließend Zementieren der Femurkomponente mit hochviskösem Zement unter Vermeidung von Hammerschlägen. Verifikation der Implantatposition durch das Navigationssystem; Entfernung der Schanz-Schraube, Gelenkreposition und Wundverschluss in üblicher Weise.WeiterbehandlungMobilisation an zwei Unterarmgehstützen mit 20 kg Teilbelastung für 2 Wochen, Belastung mit halbem Körpergewicht bis zur 6. Woche, anschließend Vollbelastung und Freigabe.ErgebnisseDer Vergleich von 40 navigierten und 32 konventionell implantierten ASR®-Prothesen ergab eine signifikante Reduktion von Ausreißern durch die Computernavigation (navigiert: ein Ausreißer, konventionell: neun Ausreißer; p < 0,001). Zwischen geplanter und verifizierter, navigierter Implantatposition wurden eine Abweichung des CCD-Winkels von 1° sowie eine Differenz der Antetorsion von 1° und des Offsets von 1,5 mm gemessen. Eine weiterführende computertomographiebasierte anatomische Studie konnte eine Genauigkeit des Navigationssystems in der Frontalebene von 1° nachweisen.AbstractObjectivePrecise implantation of hip resurfacing arthroplasty by imageless computer navigation. Hence a malalignment of the femoral component, leading to early loss of the implant, can safely be avoided.IndicationsCoxarthrosis in patients with normal bone mineral density; only minor deformity of the femoral head that enables milling around the femoral neck without notching.ContraindicationsOsteoporosis; large necrosis of the femoral head; metal allergy; small acetabular seat and corresponding wide femoral neck, leading to needless acetabular bone loss; pregnancy, lactation.Surgical TechniqueHip joint exposure by a standard surgical approach, bicortical placement of a Schanz screw for the navigation array in the lesser trochanter. Referencing of the epicondyles, the four planes around the femoral neck and head by use of the navigation pointer. Planning of the desired implant position on the touchscreen of the navigation device; a guide wire is inserted into the femoral head and neck using the navigated drill guide; navigated depth drilling is performed. The femoral head is milled using the standard instruments. The acetabular bone stock is prepared with the conventional instrumentation; high-viscosity cement is finger-packed on the reamed head and the femoral component is inserted. Hammer blows should be avoided to prevent microfractures. Verification of the implant position by the navigation device; displacement of the Schanz screw; joint reposition and closure of the wound.Postoperative ManagementStandard postoperative management after hip arthroplasty.ResultsThe comparison of 40 navigated and 32 conventionally implanted ASR® prostheses resulted in a significant reduction of outliers by use of computer navigation (navigated procedures: one outlier, conventional procedure: nine outliers; p < 0.001). Accuracy of the navigation device was tested by analysis of planned and verified implant position: CCD angle accuracy was 1°, antetorsion accuracy was 1°, and offset accuracy was 1.5 mm. An ongoing computed tomography- based anatomic study proved a varus-valgus accuracy of the navigation device of 1°.

Comparison of the Manchester–Oxford Foot Questionnaire (MOXFQ) and the Self-Reported Foot and Ankle Outcome Score (SEFAS) in patients with foot or ankle surgery

BACKGROUND Patient-reported outcome measures are a critical tool in evaluating the efficacy of orthopedic procedures. The intention of this study was to compare the psychometric properties of the Manchester-Oxford Foot Questionnaire (MOXFQ) and the Self-Reported Foot and Ankle Outcome Score (SEFAS) in patients with foot or ankle surgery. METHODS 177 patients completed both scores and FAOS, Foot and Ankle Outcome Score (FAOS), Short Form 36 (SF-36) and numeric scales for pain and disability (NRS) before and after surgery. Test-Retest reliability, internal consistency, floor and ceiling effects, construct validity, responsiveness and minimal important change were analyzed. RESULTS The MOXFQ and SEFAS demonstrated excellent test-retest reliability with interclass correlation coefficient values >0.9 Cronbachs alpha (α) values demonstrated strong internal consistency. No floor or ceiling effects were observed for both questionnaires. As hypothesized MOXFQ subscales correlated strongly with corresponding SEFAS, FAOS and SF-36 domains. MOXFQ subscales showed excellent responsiveness between preoperative assessment and postoperative follow-up, whereas SEFAS demonstrated moderate responsiveness. CONCLUSIONS The MOXFQ and SEFAS demonstrated good psychometric properties and proofed to be valid and reliable instruments for use in foot and ankle patients. MOXFQ showed better outcomes in responsiveness.

Aktuelle diagnostische und therapeutische Vorgehensweise bei Hallux-valgus-Deformität – Ergebnisse einer bundesweiten Umfrage und Vergleich mit der internationalen Literatur

BACKGROUND Hallux valgus is one of the most prevalent foot deformities, and surgical treatment of Hallux valgus is one of the most common procedures in foot and ankle surgery. Diagnostic and treatment standards show large variation despite medical guidelines and national foot and ankle societies. The aim of this nationwide survey is a description of the current status of diagnostics and therapy of Hallux valgus in Germany. MATERIAL AND METHODS A nationwide online questionnaire survey was sent to two German foot and ankle societies. The participants were asked to answer a questionnaire of 53 questions with four subgroups (general, diagnostics, operation, preoperative management). Surgical treatment for three clinical cases demonstrating a mild, moderate and severe Hallux valgus deformity was inquired. RESULTS 427 foot and ankle surgeons answered the questionnaire. 388 participants were certified foot and ankle surgeons from one or both foot and ankle societies. Medical history (78%), preoperative radiographs (100%) and preoperative radiographic management (78%) are of high or very high importance for surgical decision pathway. Outcome scores are used by less than 20% regularly. Open surgery is still the gold standard, whereas minimally invasive surgery is performed by only 7%. CONCLUSION Our survey showed that diagnostic standards are met regularly. There is a wide variation in the type of procedures used to treat Hallux valgus deformity. TMT I arthrodesis is preferred in severe Hallux valgus, but also used to treat moderate and mild deformities. Minimally invasive surgery is still used by a minority of surgeons. It remains to be seen, to what extent minimally invasive surgery will be performed in the future.

Bildfreie Computernavigation von Hüftoberflächenersatzprothesen@@@Imageless Computer Navigation of Hip Resurfacing Arthroplasty

OBJECTIVE Precise implantation of hip resurfacing arthroplasty by imageless computer navigation. Hence a malalignment of the femoral component, leading to early loss of the implant, can safely be avoided. INDICATIONS Coxarthrosis in patients with normal bone mineral density; only minor deformity of the femoral head that enables milling around the femoral neck without notching. CONTRAINDICATIONS Osteoporosis; large necrosis of the femoral head; metal allergy; small acetabular seat and corresponding wide femoral neck, leading to needless acetabular bone loss; pregnancy, lactation. SURGICAL TECHNIQUE Hip joint exposure by a standard surgical approach, bicortical placement of a Schanz screw for the navigation array in the lesser trochanter. Referencing of the epicondyles, the four planes around the femoral neck and head by use of the navigation pointer. Planning of the desired implant position on the touchscreen of the navigation device; a guide wire is inserted into the femoral head and neck using the navigated drill guide; navigated depth drilling is performed. The femoral head is milled using the standard instruments. The acetabular bone stock is prepared with the conventional instrumentation; high-viscosity cement is finger-packed on the reamed head and the femoral component is inserted. Hammer blows should be avoided to prevent microfractures. Verification of the implant position by the navigation device; displacement of the Schanz screw; joint reposition and closure of the wound. POSTOPERATIVE MANAGEMENT Standard postoperative management after hip arthroplasty. RESULTS The comparison of 40 navigated and 32 conventionally implanted ASR prostheses resulted in a significant reduction of outliers by use of computer navigation (navigated procedures: one outlier, conventional procedure: nine outliers; p<0.001). Accuracy of the navigation device was tested by analysis of planned and verified implant position: CCD angle accuracy was 1 degrees , antetorsion accuracy was 1 degrees , and offset accuracy was 1.5 mm. An ongoing computed tomography-based anatomic study proved a varus-valgus accuracy of the navigation device of 1 degrees .ZusammenfassungOperationszielPräzise Implantation von Oberflächenersatzprothesen der Hüfte durch bildfreie Computernavigation. Vermeidung von Fehlimplantationen am Femurkopf, die ein frühes Implantatversagen bedingen könnten.IndikationenKoxarthrose bei normaler Knochendichte; geringe Deformität des Hüftkopfes, so dass ein Überfräsen des Schenkelhalses ohne dessen Verletzung möglich ist.KontraindikationenOsteoporose; ausgeprägte Hüftkopfnekrose; Nickelallergie; kleine Pfanne bei breitem Schenkelhals, so dass ein unnötiger azetabulärer Knochenverlust entstehen würde; aktuelle oder geplante Schwangerschaft, Stillzeit.OperationstechnikÜber einen dorsalen Standardzugang Darstellung des Hüftgelenks, bikortikales Einbringen einer Schanz-Schraube zur Aufnahme des Referenzsterns auf Höhe des Trochanter minor. Referenzieren der Epikondylen, aller vier Ebenen des Schenkelhalses und des Hüftkopfes mit Navigationspointer; Planung der Implantatposition am steril bezogenen Bildschirm; navigiertes Einbohren eines Führungsdrahts, navigierte Tiefenfräsung. Kanüliertes Überfräsen des Hüftkopfes. Konventionelle Implantation der Pfanne; anschließend Zementieren der Femurkomponente mit hochviskösem Zement unter Vermeidung von Hammerschlägen. Verifikation der Implantatposition durch das Navigationssystem; Entfernung der Schanz-Schraube, Gelenkreposition und Wundverschluss in üblicher Weise.WeiterbehandlungMobilisation an zwei Unterarmgehstützen mit 20 kg Teilbelastung für 2 Wochen, Belastung mit halbem Körpergewicht bis zur 6. Woche, anschließend Vollbelastung und Freigabe.ErgebnisseDer Vergleich von 40 navigierten und 32 konventionell implantierten ASR®-Prothesen ergab eine signifikante Reduktion von Ausreißern durch die Computernavigation (navigiert: ein Ausreißer, konventionell: neun Ausreißer; p < 0,001). Zwischen geplanter und verifizierter, navigierter Implantatposition wurden eine Abweichung des CCD-Winkels von 1° sowie eine Differenz der Antetorsion von 1° und des Offsets von 1,5 mm gemessen. Eine weiterführende computertomographiebasierte anatomische Studie konnte eine Genauigkeit des Navigationssystems in der Frontalebene von 1° nachweisen.AbstractObjectivePrecise implantation of hip resurfacing arthroplasty by imageless computer navigation. Hence a malalignment of the femoral component, leading to early loss of the implant, can safely be avoided.IndicationsCoxarthrosis in patients with normal bone mineral density; only minor deformity of the femoral head that enables milling around the femoral neck without notching.ContraindicationsOsteoporosis; large necrosis of the femoral head; metal allergy; small acetabular seat and corresponding wide femoral neck, leading to needless acetabular bone loss; pregnancy, lactation.Surgical TechniqueHip joint exposure by a standard surgical approach, bicortical placement of a Schanz screw for the navigation array in the lesser trochanter. Referencing of the epicondyles, the four planes around the femoral neck and head by use of the navigation pointer. Planning of the desired implant position on the touchscreen of the navigation device; a guide wire is inserted into the femoral head and neck using the navigated drill guide; navigated depth drilling is performed. The femoral head is milled using the standard instruments. The acetabular bone stock is prepared with the conventional instrumentation; high-viscosity cement is finger-packed on the reamed head and the femoral component is inserted. Hammer blows should be avoided to prevent microfractures. Verification of the implant position by the navigation device; displacement of the Schanz screw; joint reposition and closure of the wound.Postoperative ManagementStandard postoperative management after hip arthroplasty.ResultsThe comparison of 40 navigated and 32 conventionally implanted ASR® prostheses resulted in a significant reduction of outliers by use of computer navigation (navigated procedures: one outlier, conventional procedure: nine outliers; p < 0.001). Accuracy of the navigation device was tested by analysis of planned and verified implant position: CCD angle accuracy was 1°, antetorsion accuracy was 1°, and offset accuracy was 1.5 mm. An ongoing computed tomography- based anatomic study proved a varus-valgus accuracy of the navigation device of 1°.