[Trends in navigation-handheld systems]. / Trends in der Navigation ­ Handheld-Systeme.

Navigation-assisted surgical procedures in orthopedics and trauma surgery have become increasingly widespread over the last 20 years. In addition to applications in spinal surgery, they are primarily available for knee and hip endoprosthetics. On the one hand, computer-assisted procedures have been increasingly expanded with robotic assistance systems in recent years, and on the other hand, so-called handheld navigation systems have been developed, which enable specialized use directly in the operating field at lower acquisition costs. The aim of this overview is to describe current handheld systems and to present the respective technical principles and the available scientific results. Three handheld systems for TKA use, two for THA use and one system to support pedicle screw placement on the spine are presented.

Leg axis correction with ConforMIS iForma (interpositional device) in unicompartmental arthritis of the knee.

Degeneration of the meniscus and the articular cartilage in unicompartmental osteoarthritis of the knee results in progressive deformity of the leg axis. It is the aim of this study to evaluate if a leg axis correction can be achieved by implanting a customised metallic interpositional device for the knee (ConforMIS iForma). Before and after implanting a ConforMIS iForma knee implant, a radiological analysis of the leg axis deviation in the frontal plane was performed prospectively in 27 patients by evaluating anteroposterior single-leg stance radiographs. We achieved a sufficient leg axis correction with an average correction of 3.8 degrees and an averaged small under-adjustment of 0.9 degrees by inserting the ConforMIS iForma interpositional knee implant. Apart from the primary treatment objective of articular surface restitution the ConforMIS iForma knee implant can be reliably used to correct axis deformity occurring with unicompartmental osteoarthritis of the knee.

Cementing technique in femoral resurfacing.

INTRODUCTION: The cementing technique is one of the various speculated factors that might contribute to the failures of resurfacing arthroplasty of the hip. The influence of bony preparation by jet lavage or lavage only in combination with different cementing techniques and cements of different viscosity in a study on fresh human femoral heads has not been evaluated so far. MATERIALS AND METHODS: Sixty fresh human femoral heads were prepared for resurfacing following manufacturers' instructions and divided into 12 groups. The different groups received either syringe lavage or jet lavage and either a low-, medium- or high-viscosity cement with either packing or quarter filling of the implant with recess of the femoral stem in each case. Application of the implant was standardized. After polymerization, the femoral heads were cut into quarters and polished. Cement penetration was assessed using a square millimeter grid under optical zoom. RESULTS: Manual packing with high viscosity cement is a reproducible method in resurfacing arthroplasty. Syringe lavage and jet lavage mainly showed comparable cement penetration patterns when applied same cementing techniques. The penetration depth ranged from a mean of 0.6 to 3.2 mm with 0.4 being the lowest and 4.0 being the deepest. The mantle thickness ranged from 0.8 to 2.4 mm with statistically significant thicker mantles with filling, compared to packing. CONCLUSION: Our results showed distinct less penetration depth than previously reported and that just medium viscosity cement reached reliable results in the supposed range of penetration depth and cement mantle thickness. Jet lavage should be recommended for the low-viscosity cement but avoided in combination with a cement filling technique of lower viscosity cements. Filling of the implant caused the greatest penetration depth and a higher number of incomplete seatings and should therefore be avoided.

Fluoroscopically based drilling of the femoral head in a model of adiposis.

OBJECTIVE: Exact drilling into the ischemic areas of necrotic lesions of the femoral head remains a challenging procedure, particularly in obese patients. This study was conducted to evaluate the precision of fluoroscopically based drilling and the associated radiation exposure in an in-vitro model of adiposis. MATERIALS AND METHODS: In an in-vitro model of necrotic lesions in adiposis, 20 sawbones were drilled under the guidance of an intraoperative navigation system (VectorVision, BrainLAB, Munich, Germany) and 20 more were drilled conventionally under fluoroscopic control only. RESULTS: A statistically significant difference was found with respect to the distance from the drill tip to the desired mid-point of the lesion, with a mean distance of 0.56 mm for the navigated group and 1.15 mm for the control group. Furthermore, a significant difference was found in the number of drilling corrections required, as well as the radiation exposure time: The navigated group required a mean of 0.35 second drillings or corrections of the drilling direction, compared to 2.45 for the control group, and the duration of radiation exposure was less than 1 second for the navigated group and 3.85 seconds for the control group. CONCLUSIONS: Drilling guided by the VectorVision navigation system shows high precision, even under difficult circumstances such as those encountered in adiposis, with a marked reduction in the duration of radiation exposure.

The effect of femoral component rotation on patellar tracking in total knee arthroplasty.

Rotational adjustment of the femoral component in total knee arthroplasty influences patellar tracking. Sixty patients underwent TKA; the femoral component was placed parallel to the epicondylar axis in 30 patients and the femoral component was placed in 3 degrees external rotation to the posterior condylar axis in 30 patients. The epicondylar axis was identified using an image-guided navigation system. Mean patellar shift was 2.65 degrees for the computer assisted group and 3.50 degrees for the control group. Mean patellar tilt was 4.88 degrees for the computer assisted group and 6.68 degrees for the control group. Aligning the femoral component parallel to the epicondylar axis leads to significantly better patellar tracking.

Position of the acetabular cup -- accuracy of radiographic calculation compared to CT-based measurement.

OBJECTIVE: A variety of mathematical and trigonometric methods has been described for determining the position of the acetabular cups from conventional radiographs. However, these formulae are subject to unduly large inaccuracies. The aim of the study was to compare the reliability and the accuracy of radiological and CT-based determination of acetabular cup position. MATERIALS AND METHODS: The positions of acetabular cups of 31 patients were calculated in conventional plain radiographs of the hip using the method described by Widmer. Further, in all patients computed tomograms of the pelvis were performed and the cup position was measured with the aid of a CT-based computer-assisted navigation software. As reference values inclination and anteversion of the cups were calculated in 3D reconstructions of the pelvis with the aid of an image processing software. RESULTS: The radiological measurement as well as the CT-based method showed good intra- and inter-observer reliability and no significant difference in the calculation of the inclination (p=0.409). However, CT-based determination of anteversion was significantly more exact than radiological measurement (p<0.001). The calculation of the cup anteversion from the X-rays showed serious deviations from the reference method and a substantial error range (X-ray: mean deviation +1.74 degrees, range -16.6 degrees to +29.8 degrees , S.D. +/-9.32 degrees; CT-based: mean deviation -0.74 degrees, range -6.6 degrees to +5.3 degrees, S.D. +/-2.87). CONCLUSION: For any clinical problem or for clinical studies in which acetabular positions of acetabular cups have to be exactly determined, CT-based measuring methods are obviously the method of choice. Evaluations based only on conventional plain X-rays and calculation of the acetabular cup position using the formula described by Widmer must be regarded as unreliable, particularly, because of problems in measuring the anteversion.

Implementation of a CT-based navigation system in two-stage reimplantation for infected total knee arthroplasty.

Femorotibial alignment is an important factor affecting patient outcome after total knee arthroplasty (TKA). It was the aim of this study to report our first results using a CT-based navigation system in two-stage revision surgery for infected TKA. Two patients with chronic deep infection after primary TKA underwent two-stage revision arthroplasty with temporary articulating cement spacers followed by prosthesis re-implantation using a CT-based navigation system. Postoperative radiographs showed accurate alignment of the femoral and tibial components. CT-based navigation systems offer the opportunity for preoperative planning and accurate intra-operative navigation of cutting blocks. They can be considered of value for primary TKA but even more so for two-stage revision arthroplasty.

Computer-assisted total knee arthroplasty versus the conventional technique: how precise is navigation in clinical routine?

Restoration of the mechanical leg axis and component positioning are crucial factors affecting long-term results in total knee arthroplasty (TKA). In a prospective study, 1,000 patients were operated on either using a CT-free navigation system or the conventional jig-based technique. Leg alignment and component orientation were determined on postoperative X-rays. The mechanical leg axis was significantly better in the computer-assisted group (95%, within +/-3 degrees varus/valgus) compared to the conventional group (74%, within +/-3 degrees varus/valgus) (P < 0.001). On average, the operating time was increased by 8 min in the computer-assisted group. No significant differences were seen between senior and younger surgeons regarding postoperative leg alignment and operating time. Computer-assisted TKA leads to a more accurate restoration of leg alignment and component orientation compared to the conventional jig-based technique. Potential benefits in long-term outcome and functional improvement require further investigation.

The effectiveness of sequential medial soft tissue release on coronal alignment in total knee arthroplasty: using a computer navigation model.

Soft tissue management is a major step in total knee arthroplasty. We aimed to analyze the relationship between sequential medial soft tissue release and the resulting change in the anteroposterior limb axis and the tibiofemoral gaps. Measurements were obtained using a CT-free navigation system (Ci navigation system, DePuy I-Orthopaedics, Munich, Germany). Concerning leg axis, each release step led to significant (P < .001) effects. The highest effect was seen for the 6-cm release in extension and the release of medial collateral ligament in 90 degrees flexion. The medial gap difference was significant for each release step except the 4-cm release in extension. The highest increase resulted when sacrificing the entire posterior cruciate ligament in extension and in 90 degrees flexion. Implementation of computer-assisted surgery allows this first navigation-controlled study, elucidating the effect of soft tissue release in total knee arthroplasty.

Gap configuration and anteroposterior leg axis after sequential medial ligament release in rotating-platform total knee arthroplasty.

BACKGROUND: Soft tissue management is a major issue in total knee replacement. There have been very few papers dealing with its effect on leg axis and tibiofemoral gap. METHODS: In a cadaver specimen study, we analyzed this effect by performing a sequential medial soft tissue release after a mobile-bearing total knee arthroplasty. Measurements were obtained using a CT-free navigation system (Ci navigation system). RESULTS: We found the highest increase in leg axis and medial gap when releasing the anteromedial tibial sleeve of the capsule 6 cm below the joint line, in extension, and after dividing the medial collateral ligament, in flexion, when releasing the medial half of the posterior cruciate ligament. There were differences in amount of change between extension and flexion, especially when releasing the medial half of the posterior cruciate ligament. In extension, the lateral gap remained the same as in flexion. INTERPRETATION: Implementation of computer-assisted surgery has allowed this first navigation-controlled study investigating the effect of soft tissue release in TKR with rotating platform. Each sequential release step has the desired effect on a.p. leg axis and tibiofemoral gaps. It is important that the differences between the effects in extension and flexion be noted.

Revision total knee arthroplasty: a comparison of postoperative leg alignment after computer-assisted implantation versus the conventional technique.

Accurate reconstruction of leg alignment is one important factor for long-term survival in total knee arthroplasty (TKA). Recent developments in computer-assisted surgery focused on systems improving TKA. The aim of the study is to compare the results of computer-assisted revision TKA with the conventional technique. We hypothesize that a significantly better leg alignment and component orientation is achieved when using a navigation system for revision TKA. In a prospective study, two groups of 25 revision TKAs each were operated on using either a CT-free navigation system or the classical surgeon-controlled technique. The postoperative leg alignment was analysed on long-leg coronal and lateral X-rays. The mechanical limb axis was significantly better in the navigation-based group. Twenty-three patients (92%) in the computer-assisted group had a postoperative leg axis between 3 degrees varus/valgus deviation, while 19 patients (76%) in the conventional group had a comparable result (p<0.05). Further, significant differences were seen for the coronal orientation of the femoral component. Computer-assisted revision TKA leads to a superior restoration of leg alignment compared with the conventional technique. Particularly the real-time presentation of the actual leg axis and the flexion and extension gaps is useful in revision TKA. Potential benefits in long-term outcome and functional improvement require additional investigation.

Computer-assisted cannulated screw fixation for slipped capital femoral epiphysis.

In slipped capital femoral epiphysis (SCFE), cannulated screw fixation is a standard procedure. The aim of this study was to investigate the feasibility of a fluoroscopy-supported navigation system for screw fixation in SCFE. Using a fluoroscopy-enhanced navigation system, a cannulated screw fixation was performed in seven hips of four patients. The navigation system showed a high feasibility in instrument visualization and implant placing. The mean x-ray time was 6.2 seconds. Initial experiences are very promising and show advantages of the fluoroscopy-supported navigation. Considerably reduced x-ray exposure for patients and surgeons is possible. In the future, further efforts will be necessary to develop navigation-specific instruments to enhance the precision of screw positioning.

Midvastus approach in total knee arthroplasty: a randomized, double-blinded study on early rehabilitation.

The medial parapatellar approach has become the standard technique in total knee arthroplasty (TKA). However, recent studies have reported superior results regarding functional recovery when using the midvastus approach. It was the aim of this study to evaluate the early functional outcome of both surgical techniques. In a prospective, double-blinded, randomized study, 50 patients for TKA were consecutively operated on either by the medial parapatellar or the midvastus approach. Exclusion criteria were defined as previous open knee surgery and leg deformity of more than 10 degrees varus or valgus. TKA was performed in all patients by one surgeon using the same type of implants in both groups. Pain scores (VAS) were documented and follow-up data including quadriceps strength and proprioception were obtained 3 weeks and 6 weeks postoperatively. Both groups were comparable in preoperative demographic data. Postoperatively, patients in the midvastus group demonstrated significantly lower pain in rest (VAS: mean 2.25 vs. 3.03) and under movement (VAS: mean 2.92 vs. 3.13). Further, they showed superior isometric quadriceps strength at 3 weeks (41.4 vs. 27.6 Nm) and 6 weeks (47.6 vs. 35.5 Nm). Moreover, this group showed a superior postoperative proprioception, while the range of motion was similar in both groups. The midvastus approach offers advantages over the standard parapatellar arthrotomy, in the early rehabilitation period. No adverse effects were observed associated with this approach. Therefore, the midvastus approach should be considered as a valuable alternative in TKA.

Navigation-assisted, minimally invasive implant removal following a triple pelvic osteotomy.

INTRODUCTION: Triple pelvic osteotomy is known as a surgical option in young patients suffering from severe hip dysplasia. In most patients, implant removal is performed after bony consolidation. Due to the pelvic anatomy, the conventional technique is often associated with soft-tissue damage and high X-ray exposure. Recent developments in the field of computer-assisted surgery may offer new alternatives. The aim of this case report was to investigate the feasibility of a fluoroscopy-supported navigation system for the implant removal after a triple pelvic osteotomy. MATERIALS AND METHODS: Using the BrainLAB-VectorVision, a fluoroscopy-enhanced navigation system, implants were removed in a 24-year-old female patient 14 months after a triple pelvic osteotomy. RESULTS: The navigation system showed a high feasibility in the instrument visualisation and implant localisation. The screws could be precisely located, simultaneously in different X-ray planes. The total X-ray exposure time was low, totalling 17 s. CONCLUSION: Initial experiences are very promising and show impressively the advantages of fluoroscopy-supported navigation for minimally invasive implant removal. A considerably reduced X-ray exposure for patient and surgeon is possible. The removal of the inserted screw is possible through a stitch incision, with reduced OR trauma and a quicker reconvalescence.

Navigation in total-knee arthroplasty: CT-based implantation compared with the conventional technique.

Background Exact axial limb alignment in total-knee arthroplasty (TKA) is important for a successful outcome. We evaluated the efficiency of computer-assisted implantation in TKA and compared it with the classical surgeon-controlled technique. Patients and methods We implanted 100 TKA using either the computer-assisted technique (50) or the conventional approach (50). There were no significant differences between the groups regarding the preoperative leg deformity. Accuracy of implantation was determined in postoperative long-leg coronal and lateral radiographs. Results A postoperative leg axis between 3 degrees varus and 3 degrees valgus was achieved in 46 patients in the group with computer-assisted implantation and 36 patients in the control group (p=0.01). A significant difference was also seen for the femoral component alignment in frontal plane. No complications influencing the clinical outcome were observed. Interpretation A CT-based navigation system improves the accuracy of TKA, but higher costs and time-consuming planning will mean that its usage is limited to special cases. Additional tools such as ligament balancing, which are presently only available with the CT-free software module, require to be added to the CT-based system.

Efficacy of extracorporal shock-wave treatment for calcific tendinitis of the shoulder: experimental and clinical results.

The effects of various extracorporal shock wave energy levels and impulse rates were investigated using an in vitro model. In addition, we performed a controlled, randomized study to examine the clinical outcome after treatment for calcific tendinitis of the shoulder. Two groups of 40 patients each received 2000 impulses twice with an energy flux density of 0.23 mJ/mm(2) and then 0.42 mJ/mm(2). The results were evaluated by the Constant and Murley score. Disintegration of the implanted deposits requires an energy of at least 0.42 mJ/mm(2) and 2000 impulses. The clinical trial showed resorption of calcific deposits in 37.5% (0.23 mJ/mm(2)) and 55.0% (0.42 mJ/mm(2)). After 1 year the Constant and Murley score increased from 46 to 68 at 0.23 mJ/mm(2) and from 48 to 73 points at 0.42 mJ/mm(2). Based on our experimental and clinical results it is evident that disintegration of calcific deposits is dose-dependent. Because of the time that elapses until changes became evident on the radiographs, an instant and sole mechanical effect on the calcific deposits is unlikely. Therefore, a combined mechanical and cellular mechanism for absorption of the calcific deposits must be presumed.