High Femoral Antetorsion Is a Major Risk Factor for Anterior Knee Pain whereas Trochlea Dysplasia Predisposes for Patella Dislocation.

PURPOSE OF THE STUDY Patellofemoral stability and congruency are influenced by different parameters. Their contribution to anterior knee pain and instability is not fully understood. We investigated, if isolated femoral antetorsion of more than 25° leads to patellofemoral instability. MATERIAL AND METHODS We analyzed 90 knees in patients with patellofemoral complaints and correlated clinical and radiological characteristics. Patients presenting at our center between January 2018 and December 2020 because of patellofemoral pain or instability were included, provided that there was no previous surgical intervention done. RESULTS The severity of trochlea dysplasia classified using the Oswestry-Bristol classification significantly correlated with events of patellofemoral dislocations. (χ=8.152, p=0.043, φ=0.288). All males with a history of patella dislocation had at least a mild trochlea dysplasia. The majority of females complaining about patellofemoral symptoms in general had a dysplastic trochlea. Patella alta is more frequently found in patients with trochlea dysplasia than in patients with a normal femoral trochlea anatomy. DISCUSSION The majority of unstable patellofemoral joints showed a dysplastic trochlea. A high femoral antetorsion was found to be an additional minor factor contributing to instability. Isolated high femoral antetorsion without trochlea dysplasia rather leads to anterior knee pain without patella dislocation. Furthermore, no direct significant correlation between patella alta and patellofemoral instability was found. Patella alta can therefore rather be seen as a result of a dysplastic trochlea than a primary major risk factor for patellofemoral instability. CONCLUSIONS Trochlea dysplasia is the major risk factor for patellofemoral instability. Patella alta can rather be seen as a result of a dysplastic trochlea than as a primary risk factor for patella instability or pain. Isolated high femoral antetorsion often leads to patellofemoral pain syndrome but not to patella dislocations. Key words: MPFL, patella instability, patellofemoral instability.

The Association between Constitutional Knee Alignment and the Horizontal Orientation of the Ankle Joint Line.

PURPOSE OF THE STUDY To characterize constitutional frontal alignment of the ankle in genua vara, valga, and norma. MATERIAL AND METHODS Long-leg standing radiographs of 589 patients presenting between 2011 and 2020 for knee-complaints because of any reason were chosen from our database. Cases with fractures or history of bony-realignment-surgeries were excluded. The Hip-Knee-Ankle angle (HKA), the mechanical Lateral Distal Tibia Angle (mLDTA), and the Tibia-Plafond-Horizontal-Orientation angle (TPHA) were measured in 354 patients. For this study, neutral frontal alignment of the leg was defined as HKA between -3.0° and +4.0°. HKA-values <-3.0° were defined as genua valga and values >4.0° were defined as genua vara. According to these cutoffs, data was categorized into the following three patient groups: genua vara (n=157), genua norma (n=106), genua valga (n=91). For each group, the ankle alignment in the frontal plane was compared to the HKA. Finally, the three groups were compared to each other. RESULTS In the varus-group, the HKA-value was 6.9°±2.4°, the TPHA-value was 4.7°±3.5°, and the mLDTA-value was 87.4°±4.8°. In the neutral-group, the HKA-value was 1.8°±2.0°, the TPHA-value was 2.5°±2.9°, and the mLDTA-value was 87.2°±4.6°. In the valgus-group, the HKA-value was -6.0°±2.7°, the TPHA-value was -0.2°±4.7°, and the mLDTA-value was 85.0°±4.7°. DISCUSSION The frontal alignment of the ankle joint line depends on the overall frontal alignment of the leg. The TPHA correlates with varus or valgus alignment of the knee, but the mLDTA does not. In patients with valgus-aligned long-leg axis, the TPHA demonstrated less valgus alignment than in patients with varus-aligned long-leg axis. This knowledge is especially useful when planning osteotomies for correction of lower extremity malalignment. CONCLUSIONS During the planning process of osteotomies around the knee, the TPHA should be appreciated because it correlates with the constitutional knee alignment. Key words: valgus, varus, frontal alignment, coronal alignment, osteotomy.

Arthroscopic Minimal Invasive Treatment of Posterolateral Tibial Plateau Impression Fractures.

Posterolateral fractures of the tibial plateau are difficult to address. Malunion can lead to early posttraumatic arthritis of the knee due to instability and elevated joint reaction forces. Arthroscopically assisted percutaneous reduction facilitates visualization and avoids open approaches either directly from posterolateral or from lateral with optional extension via a lateral epicondylus osteotomy. We describe and illustrate a minimal invasive technique using an arthroscopic posterolateral viewing portal. Using this technique, we demonstrated very good clinical outcome with excellent patient satisfaction. Key words: Schatzker, tibia head fracture, knee arthroscopy, multiligamentary injury.

Feedback and Analysis System to Improve Partial Weight Bearing and Bone Healing Following Fractures and Osteotomies of the Lower Limb: Technical Note.

PURPOSE OF THE STUDY After the surgical treatment of injuries of the lower extremities or osteotomies, patients are frequently asked to partially load the affected leg during the first weeks of rehabilitation. The patient's compliance to the prescribed weight bearing limit and their ability to regain a physiological gait as soon as possible are necessary for a fast rehabilitation without complications. MATERIAL AND METHODS/RESULTS To support patients during this important phase of recovery, we developed a feedback and analysis system that is able to provide feedback concerning loading and roll over behavior to the patient. The system is based on sensor insoles to measure the amount of pressure and pressure distribution and on a smartphone application to provide realtime visual and acoustic feedback. CONCLUSIONS This newly developed device has the potential to monitor the rehabilitation phase and assist patients with lower leg injuries therefore decrease the complication rate and enable faster rehabilitation. Key words: lower limb fracture osteotomy around the knee, partial weight bearing, realtime feedback, smartphone application.

Combining ACL Reconstruction and Refixation: the Single Anteromedial Bundle Biological Augmentation and Refixation (SAMBBAR) Technique.

PURPOSE OF THE STUDY Anterior cruciate ligament (ACL) preservation surgical techniques have been rising lately. In the acute setting, proximal ACL tears and femoral avulsions of the ACL are good indications for primary repair of the ACL. However, literature shows a wide range of failure rates. An intact synovial membrane seems to be a predicational factor for the outcome of primary ACL repair. Disruption of the synovial membrane is associated with higher failure rates. We describe a surgical technique repairing the ACL in combination with a semitendinosus augmentation for proximal ACL tears with or without disruption of the synovial membrane. MATERIAL AND METHODS The procedure preserves as much of the original anatomy as possible by repairing the synovial membrane and ACL remnant to the femoral origin. To accomplish this, we have built on the so-called "Single Anteromedial Bundle Biological Augmentation (SAMBBA) technique" and developed it further to the "Single Anteromedial Bundle Biological Augmentation and Refixation (SAMBBAR) technique", which we firstly describe here. RESULTS All three patients treated with the SAMBBAR technique showed very good short-term clinical outcomes comparable with successful standard ACL reconstruction. There were no complications. Twelve months postoperatively, patients had no pain. They had normal range of motion in the affected knee without any signs of instability. DISCUSSION The SAMBBAR technique seems to be an adequate procedure to preserve as much proprioceptive native tissue as possible, while at the same time ensuring high tissue strength in order to reduce failure rates. Prospective randomized controlled trials are needed to compare the new SAMBBAR technique with standard ACL reconstruction, with the original SAMBBA technique, and with techniques of ACL refixation. CONCLUSIONS With the presented surgical procedure, it is possible to perform a standard ACL reconstruction using an autologous semitendinosus graft and at the same time preserving the tissue remnant of the ACL in all proximal tear patterns. This might contribute to improved proprioception and rehabilitation without sacrificing stability. Key words: anterior cruciate ligament, Lachman test, Ligamys, knee instability, semitendinosus tendon.

Acute MCL and ACL injuries: first results of minimal-invasive MCL ligament bracing with combined ACL single-bundle reconstruction.

BACKGROUND: There is an on-going discussion whether to operatively treat combined grade II and III lesions of the medial collateral ligament (MCL) with anterior cruciate ligament (ACL) in the acute phase rather than conservative treatment of the MCL lesion with a delayed unitary ACL replacement. Another issue is the question how to technically address these MCL lesions. The aim of this study was, therefore, to analyze the results of simultaneous ACL replacement (hamstrings) in a single-bundle technique with a simultaneous MCL ligament bracing procedure. METHODS: In this prospective non-randomized trial,, 16 patients were included with grade II and III lesions of the MCL. Surgical treatment was performed within 14 days (mean 10.4 days, SD ±2.3 days) by one single expert orthopedic surgeon using the semitendinosus tendon and Rigidfix® system for femoral and tibial fixation and 3.5 mm screws with one 1.3 mm PDS Cord for minimal-invasive MCL ligament bracing with screw fixation. Knee stability was measured with the Rolimeter® and KT-1000®. MCL stability was assessed in clinically and radiographically with valgus stress projections. RESULTS: The mean patient age was 36.4 with six female and ten male patients. There were no surgical complications such as infections or healing disturbances. Mean operation time was 64 ± 6 min. The arthrofibrosis rate was 0 %. Medial knee stability was normal in full extension for all cases with no intra-individual side-to-side difference. Radiological assessed MCL stability revealed Δ values with a mean of 1.1 ± 1.3 mm compared to the contra-lateral side. The Lachman Test revealed a side-to-side difference of 1.6 mm with the KT-1000® and 2.6 ± 0.9 mm when measured with the Rolimeter®. Subjective clinical assessment revealed good results with a mean Lysholm Score of 89.1 points. CONCLUSION: Acute ACL replacement and MCL ligament bracing with this novel technique revealed in this study good clinical results and objective restored knee stability without cases of knee stiffness or arthrofibrosis. The remarkable shortcoming is the small cohort number making further studies necessary.

[Return to sport after surgical treatment of a posterior cruciate ligament injury : A retrospective study of 60 patients]. / Rückkehr in den Sport nach operativer Versorgung einer hinteren Kreuzbandverletzung : Eine retrospektive Untersuchung von 60 Patienten.

BACKGROUND: Injuries of the posterior cruciate ligament (PCL) lead to an initial reduction of sporting activity. However, in previous studies, return to sport after operative treatment of PCL injuries has been analysed insufficiently. The aim of this study was (1) to determine the rate of return to sport in physically active patients, (2) to analyse possible changes in sporting activities and (3) to examine the influence of the severity of the initial injury. PATIENTS AND METHODS: Within a retrospective clinical and radiological follow-up at least 24 months after surgery (80.3 ± 28.2 months), 60 patients (44.8 ± 12.1 years) with surgically treated isolated or combined PCL injuries were included in the study. Pre-accidental and post-operative sporting activities were queried and compared in a standardised questionnaire. Possible differences with respect to the initial injury severity (Cooper classification) were examined. RESULTS: The return-to-sport rate of the physically active patients was 87.0 %. 17.6 % of patients with a combined PCL injury and 4.8 % of patients with isolated PCL injury were not able to return to sport. Significant reductions in the frequency of exercise (p = 0.0087), the duration of exercise (p = 0.0003) and the amount of regularly performed sports (p < 0.0001) were found. A change from high-impact sports to low-impact sports was noted. CONCLUSION: Patients with operatively treated PCL injuries can return to sport. However, for competitive athletes an injury to the PCL can lead to the end of their career. A reduction of sporting activities and a change from high-impact sports to low-impact sports can be expected. A persisting inability to return to sporting activities in patients with isolated PCL injuries cannot be assumed.

[The Pitch Angle of a Locked Plate Osteosynthesis Construct]. / Der Nickwinkel einer winkelstabilen Plattenosteosynthese.

UNLABELLED: The aim of the present study is to describe the biomechanical properties of the fracture motion of a locked plate construct. METHOD: The three dimensional fracture motion of a conventional and of a dynamic locked plate construct was observed using an optical measurement system. RESULTS: Fracture motion was described in terms of delta z (mean fracture motion in direction of force application) and the pitch angle (angle between the upper and lower cylinders of osteosynthesis). It could be shown that the fracture motion of a conventional locked plate construct is only possible through the bending of the plate. The ratio of pitch angle and mean fracture motion (delta z) is a measure of the necessary degrees of bending per millimeter fracture motion. At the same pitch angle, dynamic osteosynthesis gave greater fracture motion. CONCLUSION: With the parameters of pitch angle and mean fracture motion (delta z), it is possible to describe the whole fracture motion of locked plate fixation. Furthermore, it is possible to compare different locked plate constructs or fracture motions.

New Method for Monitoring Partial Weight Bearing (PWB) of Outpatients with an Independent Insole Sensor System.

UNLABELLED: PURPOSE OF THE STUDY Partial weight bearing (PWB) is commonly prescribed post operatively following lower limb fractures and compliance with the weight bearing protocol is an essential element of the rehabilitation. So far it is unknown to what extent patients do comply with PWB during the healing process as instructed by the surgeon. Our aim is to assess a new device for real-time feedback and long-term measurement of PWB of outpatients. The device offers the possibility to monitor the outpatient's activity. The applicability, reliability and validity of the new device should be evaluated. MATERIAL AND METHODS 20 young, healthy subjects complete a course of 500 m that contained several stairs, with a PWB of 15 kg. During the entire test, the axial load, the acceleration and the temperature were measured with a novel insole sensor system. The results were compared with reference measurements performed with a force plate. RESULTS Altogether, the 20 subjects performed 11,106 steps during the completion of the walking circuit. In 23.6% of the steps, the subjects applied a PWB of 10 to 20 kg. In 5.5% of all steps, PWB was superior to 60 kg. The mean bias of the insole was 11,58 N. Limits of agreement were +/- 125 N and the interclass correlation coefficient was r = 0.945. CONCLUSIONS The presented sensor sole might be a useful tool to obtain more precise insight of outpatients' activity and load to the injured limb during the healing process. Furthermore, these results demonstrate that even young and healthy subjects are not able to keep the prescribed PWB. This raises the question, if patients who have been recently operated are able to follow the instructions concerning the PWB. KEY WORDS: partial weight bearing (PWB), insole sensor system, sensor sole, monitoring, outpatients.

Surgical accuracy in high tibial osteotomy: coronal equivalence of computer navigation and gap measurement.

PURPOSE: Medial opening wedge high tibial osteotomy (MOW HTO) is now a successful operation with a range of indications, requiring an individualised approach to the choice of intended correction. This manuscript introduces the concept of surgical accuracy as the absolute deviation of the achieved correction from the intended correction, where small values represent greater accuracy. Surgical accuracy is compared in a randomised controlled trial (RCT) between gap measurement and computer navigation groups. METHODS: This was a prospective RCT conducted over 3 years of 120 consecutive patients with varus malalignment and medial compartment osteoarthritis, who underwent MOW HTO. All procedures were planned with digital software. Patients were randomly assigned into gap measurement or computer navigation groups. Coronal plane alignment was judged using the mechanical tibiofemoral angle (mTFA), before and after surgery. Absolute (positive) values were calculated for surgical accuracy in each individual case. RESULTS: There was no significant difference in the mean intended correction between groups. The achieved mTFA revealed a small under-correction in both groups. This was attributed to a failure to account for saw blade thickness (gap measurement) and over-compensation for weight bearing (computer navigation). Surgical accuracy was 1.7° ± 1.2° (gap measurement) compared to 2.1° ± 1.4° (computer navigation) without statistical significance. The difference in tibial slope increases of 2.7° ± 3.9° (gap measurement) and 2.1° ± 3.9° (computer navigation) had statistical significance (P < 0.001) but magnitude (0.6°) without clinical relevance. CONCLUSION: Surgical accuracy as described here is a new way to judge achieved alignment following knee osteotomy for individual cases. This work is clinically relevant because coronal surgical accuracy was not superior in either group. Therefore, the increased expense and surgical time associated with navigated MOW HTO is not supported, because meticulously conducted gap measurement yields equivalent surgical accuracy. LEVEL OF EVIDENCE: I.

[Lateral hinge fractures in open wedge high tibial osteotomy]. / Die Fraktur der Gegenkortikalis bei der aufklappenden Osteotomie des Tibiakopfes.

BACKGROUND: Open wedge high tibial osteotomy (HTO) is an increasingly more common surgical method. A typical problem of this procedure is fracture of the lateral hinge. OBJECTIVES: The aims of this article are to present the special issue of fractures of the lateral hinge after HTO and to discuss surgical hints on how to prevent and treat this problem. METHODS: The results of recently published clinical studies are summarized and tips from own clinical experiences are given. RESULTS: Type II fractures of the lateral hinge are unstable and can create a major problem. Using short spacer plates results in a problem of stability for all types of fractures. CONCLUSION: The classification into Takeuchi grades I-III has been proven to be suitable for fractures of the lateral hinge. The TomoFix plate is a safe implant to stabilize the osteotomy in type I and III fractures with which healing can be achieved with no problems. Type II fractures can be stabilized with the TomoFix plate; however, an autologous bone graft has to be taken into consideration. For fractures of the lateral hinge short spacer plates are not recommended due to stability issues.

[Vacuum shoe system vs.forefoot offloading shoe for the management of metatarsal fractures. A prospective, randomized trial]. / Abrollende Vakuumstützorthese versus Vorfulssentlastungsschuh zur Behandlung von Metatarsalefrakturen. Eine prospektive, randomisierte Untersuchung.

BACKGROUND: Metatarsal fractures are managed using different types of forefoot offloading orthosis. Theaim of this prospective study was to evaluate the clinical and pedographic results of a vacuum shoe system in comparison to a forefoot unloading shoe. METHOD: 20 patients (14 women/6 men--age: 36.4 +/- 14.1 years) were prospectively included in the study. The patients were followed up at four different time points. Detailed clinical and radiological examinations were carried out, functional scores were measured and a pedographic assessment was performed. RESULTS: Between the study groups no differences were seen in functional scoring. A complete bony healing was achieved within the 3 months of followup in all patients. The heelstrike to heelstrike time was without significant differences in the pedographic analysis. Adequate forefoot unloading was achieved with both orthosis. The load sharing between fore-, mid- and hindfoot showed no significant differences in the pedographic analysis. Patients' satisfaction was rated with higher values for the vacuum shoe system, but without significance. CONCLUSION: Both shoe systems show an adequate unloading of the forefoot. Therefore both orthosis may be used for the treatment of metatarsal fractures.

[Use of Bone Morphogenetic Proteins (BMPs) for the Treatment of Pseudarthroses - Efficiency and Therapy Failure]. / Einsatz der Bone morphogenetic Proteins (BMPs) zur Behandlung von Pseudarthrosen - Effizienz und Therapieversagen.

In the therapy for pseudarthroses of the proximal tibia, the human recombinant bone morphogenetic proteins (BMP-2 and BMP-7) have been used for several years. Despite their limited and specified use as local mediators of bone healing, no conclusions regarding the therapeutic success can be made beforehand. The regulatory mechanisms have turned out to be much more complex and patient-specific than had been assumed before. To help understand the cell biological processes (signalling) and the current possibilities of predicting a successful use of BMP, this article summarises the relevant findings.

[A new anatomical wing plate for osteoporotic acetabular fractures: biomechanical testing and first clinical experience]. / Die neue anatomische Flügelplatte für osteoporotische Azetabulumfrakturen: biomechanische Testung und erste klinische Erfahrungen.

BACKGROUND: Acetabular fractures are rare injuries, but there is an increasing number of elderly people with ventral medial instability in cases of central subluxation of the femoral head in osteoporotic acetabular fractures. Common plate osteosynthesis cannot enable medial support of the quadrilateral surface. The new "acetabular wing plate" is anatomically shaped to fix the arcuate line and the quadrilateral surface. The plate pushes the femoral head back to lateral. The aim of this study was the biomechanical comparison with common plate concepts before clinical use of the new implant. METHODS: For biomechanical testing eight artificial fracture models of the pelvis with anterior column fractures were used. They were implemented into a set-up of a one-leg stand model in the material test machine. Cyclical movements with axial pressure to the sacrum up to 250 N were given to the model. Fracture gap movement was measured with an optoelectronic 3D camera measuring system. In all pelvic models all screw holes were drilled by use of drill guides before first mechanical loading. The measurements were randomly done first with the new acetabular wing plate or with the pelvic low profile plate. Absolute and relative fracture gap movement and movements of the pelvic fragments were measured as well. RESULTS: The fracture gap movement and the fragment rotation were comparable in both groups. There was a slightly higher stability in the group of the acetabular wing plate but without statistical significance. In the pelvic low profile group two screw loosenings were found, but the models were able to be tested also with the acetabular wing plate. The new plate was clinically used in the first eight patients due to the good biomechanical results. In all cases the osteosyntheses were done by use of the Stoppa approach and the first window of the ilioinguinal approach. Application of the plate was mostly easy, the plate was also used as a reduction tool. Postoperative controls show anatomic reduction and correct implant position in all eight cases. The three month follow-up examinations confirm the continuing good reduction during fracture healing with the acetabular wing plate.

[Dynamic locking screw 5.0--first clinical experience]. / Dynamic Locking Screw 5.0--erste klinische Anwendung.

The principle of "biological" plate osteosynthesis describes the optimum interaction between mechanics and biology with the aim to achieve an uneventful consolidation of the fracture by secondary bone healing. The preservation of soft tissue and blood supply are central points in this context. Empirical values show that a too rigid internal fixation can suppress callus formation. The dynamic locking screw - DLS - allows for a decrease of the rigidity of a plate osteosynthesis. The fracture motion is positively affected. The advantages of the angular stability are not affected. In the Trauma Centre Tuebingen 35 patients were treated with the DLS5.0 in the time between November 2011 and October 2012. These first clinical cases with the use of the large fragment DLS showed good results. Handling the DLS5.0 is comparable to the conventional locking screw - LS5.0. Complications were not caused by the DLS and their application.

Combination of interfragmentary screws and locking plates in distal meta-diaphyseal fractures of the tibia: a retrospective, single-centre pilot study.

UNLABELLED: If distal tibia fractures cannot be treated with intramedullary nails, locking compression plates, such as the LCP Medial Distal Tibia Plate of Synthes, are used. Bridge plating with interfragmentary movement is the strategy for such osteosynthesis. Interfragmentary movement is difficult to predict. Too much movement leads to formation of more, but less stable callus; longer time until complete fracture healing has been reported. Interfragmentary movement can be controlled by the stability and flexibility of the osteosynthesis construct. We used interfragmentary screws to limit interfragmentary movement in certain cases. We noticed a tendency of faster fracture healing in patients with interfragment lag screw compared with those with sole bridge plating. We therefore retrospectively assessed our patients for time until clinical fracture healing (i.e., pain-free weight bearing and visible callus in both layers on conventional plain film radiographs) and callus formation. METHODS: Data (from patient chart and from regular visits) of 52 patients with fracture of the distal tibia were reviewed, of which 11 were lost to follow-up. After surgery, weight bearing was limited to 20 kg for 6 weeks and then increased in weekly intervals to the pain threshold. X-rays were taken after 3 days, 6, 12 and 24 weeks and when achieving full weight bearing. Time from surgery until ability to full weight bearing was measured and compared. Callus index was measured as quotient of callus thickness and diameter of corticalis both in a.p. and sagittal direction. Statistical evaluation was done with the Mann-Whitney U-test. RESULTS: A total of 41 patients could be analysed; of them, 30 patients had extra-articular fractures. Four patients had 43-B and seven patients had 43-C fractures. As many as 13/30 extra-articular fractures were treated with interfragmentary screws: In this group (n=11, without considering one patient with plate failure and one with pseudarthrosis) time to full weight bearing was 11.38 weeks versus 14.9 weeks without screw (n=14; without two pseudarthrosis and one deep infection) (p=0.044). Callus index at full weight bearing was significantly lesser in patients with screw compared with those without. CONCLUSION: Though interfragmentary screws seem to block necessary interfragmentary movement, we see callus formation as a sign of secondary fracture healing. The osteosynthesis construct with interfragmentary screw seems to be more stable and less flexible than sole bridge plating, leading to faster fracture healing. Interfragmentary screws might help to control and limit interfragmentary movement in certain cases.

[Therapy-resistant tibial pseudarthrosis. Treatment success with BMP-7 combined with autologous bone]. / Therapieresistente Unterschenkelpseudarthrose. Behandlungserfolg durch BMP-7, kombiniert mit autologem Knochen.

Delayed union or non-union of long bone shaft fractures still presents a surgical challenge. Especially if there is a predisposition for pseudarthrosis such as adiposity, diabetes mellitus, local disruption of blood supply or lack of hormones, the established procedures of autologous cancellous bone grafting or plate fixation with compression often lead to insufficient results. In the following article the successful use of bone morphogenetic protein BMP-7 [recombinant human osteogenetic protein-1 (rhOP-1)], combined with autologous bone grafting for therapy of a therapy-resistant tibial non-union is described. In a patient with multiple risk factors the tibial fracture was completely cured after two attempts of osteosynthesis and autologous bone grafting had failed. The patient achieved self-mobility with full weight bearing and absence of pain 10 months after adjuvant implantation of BMP-7.

Experiments on robot-assisted navigated drilling and milling of bones for pedicle screw placement.

BACKGROUND: This article presents experimental results for robot-assisted navigated drilling and milling for pedicle screw placement. The preliminary study was carried out in order to gain first insights into positioning accuracies and machining forces during hands-on robotic spine surgery. Additionally, the results formed the basis for the development of a new robot for surgery. METHODS: A simplified anatomical model is used to derive the accuracy requirements. The experimental set-up consists of a navigation system and an impedance-controlled light-weight robot holding the surgical instrument. The navigation system is used to position the surgical instrument and to compensate for pose errors during machining. Holes are drilled in artificial bone and bovine spine. A quantitative comparison of the drill-hole diameters was achieved using a computer. RESULTS: The interaction forces and pose errors are discussed with respect to the chosen machining technology and control parameters. Within the technological boundaries of the experimental set-up, it is shown that the accuracy requirements can be met and that milling is superior to drilling. CONCLUSIONS: It is expected that robot assisted navigated surgery helps to improve the reliability of surgical procedures. Further experiments are necessary to take the whole workflow into account.