C. Lüring

Alignment in total knee arthroplasty A COMPARISON OF COMPUTER-ASSISTED SURGERY WITH THE CONVENTIONAL TECHNIQUE

Restoration of neutral alignment of the leg is an important factor affecting the long-term results of total knee arthroplasty (TKA). Recent developments in computer-assisted surgery have focused on systems for improving TKA. In a prospective study two groups of 80 patients undergoing TKA had operations using either a computer-assisted navigation system or a conventional technique. Alignment of the leg and the orientation of components were determined on post-operative long-leg coronal and lateral films. The mechanical axis of the leg was significantly better in the computer-assisted group (96%, within +/- 3 degrees varus/valgus) compared with the conventional group (78%, within +/- 3 degrees varus/valgus). The coronal alignment of the femoral component was also more accurate in the computer-assisted group. Computer-assisted TKA gives a better correction of alignment of the leg and orientation of the components compared with the conventional technique. Potential benefits in the long-term outcome and functional improvement require further investigation.

Radiological results of image-based and non-image-based computer-assisted total knee arthroplasty

Restoration of the mechanical limb axis and accurate component orientation are two major factors affecting the long-term results after total knee replacement (TKR). Different navigation systems are available to improve the outcome. Image-based systems require pre-operative CT scans, while non-image-based systems gain all necessary information intra-operatively during a registration process. We studied 130 patients who received a TKR either using the CT-based (Knee 1.1) or the CT-free module (CT-free Knee 1.0) of the BrainLAB Vector-Vision Navigation System. Post-operative leg alignment and component orientation was determined on long-leg coronal and lateral X-rays. Sixty of 65 patients in the CT-based group and 63/65 patients in the CT-free group had a post-operative leg axis between 3° varus/valgus. No significant differences were found for varus/valgus orientation of the femoral and tibial components.RésuméLa restauration de l’axe mécanique du membre inférieur et l’orientation exacte des implants sont deux facteurs majeurs qui affectent les résultats à longue échéance après arthroplastie totale du genou total (PTG). Différents systèmes de navigation sont disponibles pour améliorer ces paramètres. Certains systèmes de navigation exigent une tomodensitométrie (TDM) préopératoire, tandis que d’autres acquièrent les informations nécessaires pendant l’intervention. Nous avons étudié 130 malades qui ont reçu un PTG soit avec une TDM préopératoire (Genou 1.1) soit avec le système sans TDM (BrainLAB Vecteur Vision® Navigation System), genou 1.0. L’alignement postopératoire du membre inférieur et l’orientation des composants a été déterminé sur des grands clichées coronaux et latéraux de membre inférieur. 60/65 malades dans le groupe TDM préopératoire et 63/65 malades dans le groupe sans TDM avaient un axe de membre inférieur postopératoire entre 0 et 3° de varus/valgus. Aucune différence notable n’a été trouvée concernant l’orientation des composants en varus/valgus.

Intraoperative cutting errors in total knee arthroplasty

IntroductionPrecise reconstruction of leg alignment offers the best opportunity for achieving good long-term results in total knee arthroplasty (TKA). It was the aim of this study to evaluate the bone-cutting process as a potential source of inaccuracy in TKA.Materials and methodsIn a consecutive series of 50 computer-assisted TKAs, cutting errors, which were defined as a difference between the cutting block position before sawing and the achieved resection plane afterwards, were measured for the distal femur and proximal tibia resection. Measurements were performed using a CT-based navigation system.ResultsFor the distal femoral cut, there was a mean varus/valgus deviation of 0.6° (SD±0.5°) and a mean flexion/extension deviation of 1.4° (SD±1.3°). For the proximal tibia, varus/valgus alignment showed a mean deviation of 0.5° (SD±0.5°). The mean sagittal variability was 1.0° (SD±0.9°). Differences between the frontal and the sagittal plane were significant.ConclusionTo minimize cutting errors, techniques and instruments are needed which enable a more stable fixation of the cutting blocks or even more appropriate preparation instruments. Using a computer-assisted technique, the surgeon is aware of cutting errors occurring at each point of the operation and will therefore be able to correct these errors during surgery, while he is not aware of those errors with the conventional TKA technique.

Evaluation of implant position and knee alignment after patient-specific unicompartmental knee arthroplasty

Implant positioning and knee alignment are two primary goals of successful unicompartmental knee arthroplasty. This prospective study outlines the radiographic results following 32 patient-specific unicompartmental medial resurfacing knee arthroplasties. By means of standardized pre- and postoperative radiographs of the knee in strictly AP and lateral view, AP weight bearing long leg images as well as preoperative CT-based planning drawings an analysis of implant positioning and leg axis correction was performed.The mean preoperative coronal femoro-tibial angle was corrected from 7° to 1° (p<0.001). The preoperative medial proximal tibial angle of 87° was corrected to 89° (p<0.001). The preoperative tibial slope of 5° could be maintained. The extent of the dorsal femoral cut was equivalent to the desired value of 5mm given by the CT-based planning guide. The mean accuracy of the tibial component fit was 0mm in antero-posterior and +1mm in medio-lateral projection. Patient-specific fixed bearing unicompartmental knee arthroplasty can restore leg axis reliably, obtain a medial proximal tibial angle of 90°, avoid an implant mal-positioning and ensure maximal tibial coverage.

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 hypothize 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° 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.

Cup positioning in THA: current status and pitfalls. A systematic evaluation of the literature

The correct determination of cup orientation in THA regarding the intraoperative as well as the postoperative assessment due to the pelvic tilt and rotation with inexact incorporation of the pelvis is uncertain. The anterior pelvic plane (APP) seems to be the most reliable reference frame and computer-assisted navigation systems seem to provide the best tool for correct implantation to date. For the intraoperative assessment of the APP, the exact determination of the bony landmarks is mandatory. For the standard plain radiography, standardized positioning of the patient and approximation of pelvic tilt by a lateral view are mandatory. An additional CT must be carried out for certain indications. More emphasis has to be given to the individuality of pelvic tilt and range of motion.

Fixation of revision TKA: a review of the literature

PurposeEarly aseptic loosening is a major complication in revision total knee arthroplasty (TKA). It is well accepted that intramedullary stems improve the anchoring of the prosthetic components; however, controversy still exists about the optimal fixation technique of the stems (cementless, hybrid, cemented).MethodsA literature review was carried out in the main medical databases from 1980 to 04/2010 to evaluate the available literature by evidence-based criteria and to analyse the results of the single studies regarding fixation technique in knee revision arthroplasty.ResultsThere are four studies regarding the cementless fixation. Eight studies reported the hybrid technique and five studies the cemented technique. Hybrid and cemented techniques are comparable regarding the survival of arthroplasties, the rate of aseptic loosening and the clinical outcome. However, most studies just show a low level of evidence (LoE III and IV), a small to medium number of cases and a short follow-up.ConclusionBased on the current literature, no final statement can be drawn regarding the optimal fixation technique in revision TKA. Future RCTs are needed to enable conclusive statements about the possible advantages and disadvantages of the single fixation techniques, although the clinical implementation often is critical.

CRP and leukocyte-count after lumbar spine surgery: fusion vs. nucleotomy

Background Despite the fact that C-reactive protein (CRP) levels and white blood cell (WBC) count are routine blood chemistry parameters for the early assessment of wound infection after surgical procedures, little is known about the natural history of their serum values after major and minimally invasive spinal procedures. Methods Pre- and postoperative CRP serum levels and WBC count in 347 patients were retrospectively assessed after complication-free, single-level open posterior lumbar interlaminar fusion (PLIF) (n = 150) for disc degeneration and spinal stenosis and endoscopically assisted lumbar discectomy (n = 197) for herniated lumbar disc. Confounding variables such as overweight, ASA classification, arterial hypertension, diabetes mellitus, and perioperative antibiotics were recorded to evaluate their influence on the kinetics of CRP values and WBC count postoperatively. Results In both procedures, CRP peaked 2–3 days after surgery. The maximum CRP level was significantly higher after fusion: mean 127 (SD 57) (p < 0.001). A rapid fall in CRP within 4–6 days was observed for both groups, with almost normal values being reached after 14 days. Only BMI > 25 and long duration of surgery were associated with higher peak CRP values. WBC count did not show a typical and therefore interpretable profile. Conclusion CRP is a predictable and responsive serum parameter in postoperative monitoring of inflammatory responses in patients undergoing spine surgery, whereas WBC kinetics is unspecific. We suggest that CRP could be measured on the day before surgery, on day 2 or 3 after surgery, and also between days 4 and 6, to aid in early detection of infectious complications.

Two-year follow-up on joint stability and muscular function comparing rotating versus fixed bearing TKR

Mobile and fixed bearing in total knee replacement are still discussed controversially. In a retrospective, matched-pair study, we investigated 40 patients with computer-assisted (BrainLAB®) primary total knee replacement (PFC Sigma®, DePuy®) performed two years before. Twenty patients each received a mobile bearing and a fixed bearing. We compared Womac Score, Knee Society Score, postoperative ROM, fluoroscopic measurement of knee stability in flexion and extension and isokinetic muscle strength using a BiodexTM-3 dynamometer. Both groups showed similar results concerning WOMAC Score (total rotating bearing: 23.05; fixed bearing: 22.57), KSS (rotating bearing: 174.89; fixed bearing: 176.1). Isokinetic muscle force demonstrated statistically significant superior results for knee flexion in the rotating bearing group. Medio-lateral stability revealed statistically significant superior results for the rotating bearing compared to fixed bearing in extension (P>0.05). In flexion only lateral stability was superior (P>0.05). Two-year clinical follow-up after computer-assisted total knee replacement resulted in good clinical outcome with high patient satisfaction. Statistically significant better values for the rotating platform group were found for the medio-lateral stability in extension and the peak flexion torque.

Flexion gap configuration in total knee arthroplasty following high tibial osteotomy

Previous reports have described the potentially compromising effect of a high tibial osteotomy (HTO) on the results of a subsequent total knee arthroplasty (TKA). Although the reasons are not clear, some authors reported problems in soft-tissue balancing. In a prospective study, 22 patients with an average interval of 5.8 years after closed-wedge HTO were operated for TKA. All operations were performed with a CT-free navigation system, and measurements of the extension and flexion gap were assessed. The intraoperative data were compared to a control group of 100 consecutive computer-assisted TKA without previous osteotomy. In the study group, a highly significant shift towards a medial opening of the flexion gap between the posterior condylar line and the tibial resection (study group 0.4±4.7° medial opening versus control group 3.4±3.3° lateral opening, p<0.001) was observed. In the study group, 10/22 showed a medial opening of the flexion gap compared to 11/100 in the control group. Surgeons should be aware of difficulties in soft-tissue balance in TKA following HTO, especially for the flexion gap configuration and the axial rotation of the femoral component.RésuméPlusieurs rapports ont décrit l’effet potentiellement défavorable d’une ostéotomie tibiale supérieure sur les résultats d’une arthroplastie totale du genou secondaire. Bien que les raisons ne soient pas claires, quelques auteurs ont rapporté des problèmes dans l’équilibre des parties molles. Dans une étude prospective 22 malades ont eu une arthroplastie totale du genou avec un intervalle moyen de 5,8 ans après une ostéotomie tibiale. Toutes les opérations ont été exécutées avec un système de navigation sans scanner et l’intervalle en flexion et en extension a été mesuré. Les données intraopératoires ont été comparées à un groupe témoin de 100 arthroplasties totales du genou consécutives, sous contrôle informatique, sans ostéotomie préalable. Dans le groupe d’étude a été constaté une modification très importante vers une ouverture médiale de l’intervalle en flexion entre la ligne condylienne postérieure et la résection tibiale (groupe d’étude 0,4±4,7° d’ouverture médiale contre, dans le groupe témoin, 3,4±3,3° d’ouverture latérale, p<0.001). Dans le groupe d’étude 10/22 ont montré une ouverture médiale de l’intervalle en flexion comparée à 11/100 dans le groupe témoin. Les chirurgiens doivent être conscients de la difficulté d’équilibrer les parties molles dans l’arthroplastie du genou aprés ostéotomie tibiale, surtout pour la configuration de l’intervalle en flexion et l’orientation axiale du composant fémoral.