M. Tingart

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.

Imageless navigation for insertion of the acetabular component in total hip arthroplasty: IS IT AS ACCURATE AS CT-BASED NAVIGATION?

In a prospective randomised clinical study acetabular components were implanted either freehand (n = 30) or using CT-based (n = 30) or imageless navigation (n = 30). The position of the component was determined post-operatively on CT scans of the pelvis. Following conventional freehand placement of the acetabular component, only 14 of the 30 were within the safe zone as defined by Lewinnek et al (40 degrees inclination sd 10 degrees ; 15 degrees anteversion sd 10 degrees ). After computer-assisted navigation 25 of 30 acetabular components (CT-based) and 28 of 30 components (imageless) were positioned within this limit (overall p < 0.001). No significant differences were observed between CT-based and imageless navigation (p = 0.23); both showed a significant reduction in variation of the position of the acetabular component compared with conventional freehand arthroplasty (p < 0.001). The duration of the operation was increased by eight minutes with imageless and by 17 minutes with CT-based navigation. Imageless navigation proved as reliable as that using CT in positioning the acetabular component.

Anchor Design and Bone Mineral Density Affect the Pull-out Strength of Suture Anchors in Rotator Cuff Repair Which Anchors Are Best to Use in Patients With Low Bone Quality?

Background Different metal and biodegradable suture anchors are available for rotator cuff repair. Poor bone quality may result in anchor loosening and tendon rerupture. Hypotheses Higher bone mineral density is associated with higher pull-out strength of suture anchors. Depending on anchor placement, pull-out strengths of anchors are different within the greater tuberosity. Study Design Cadaveric biomechanical study. Methods Trabecular and cortical bone mineral densities were determined for different regions within the greater tuberosity. Metal screw-type and biodegradable hook-type anchors were cyclically loaded. Results Mean failure load of metal and biodegradable anchors was 273 N and 162 N, respectively, for the proximal part (P < .01) and 184 N and 112 N, respectively, for the distal part (P < .01). Both types of anchors showed higher failure loads in the proximal-anterior and -middle parts of the greater tuberosity than in the distal part (P < .01). A significant positive correlation was found between cortical bone mineral density and failure load of metal anchors (P < .01). Conclusion Bone quality, anchor type, and anchor placement have a significant impact on anchor failure loads. Clinical Relevance Suture anchors should be placed in the proximal-anterior and -middle parts of the greater tuberosity. In the distal parts, biodegradable hook-like anchors should be used with caution.

Pullout Strength of Suture Anchors Used in Rotator Cuff Repair

BACKGROUND Surgical treatment of rotator cuff tears may be complicated by osteoporosis of the proximal part of the humerus. The purpose of this study was to determine whether pullout strength of suture anchors is affected by the location of the anchor placement and by bone mineral density. We hypothesized that higher bone mineral density is associated with higher pullout strength of suture anchors. METHODS Peripheral quantitative computed tomography was used to measure total, trabecular, and cortical bone mineral density in different regions of the lesser and greater tuberosities in seventeen cadaveric humeri. Suture anchors were inserted into individual regions and subjected to cyclic loading. Repeated-measures analysis of variance was used to assess differences in bone mineral density and load to failure between regions of interest. Pearson correlation was used to determine the association between bone mineral density and pullout strength of suture anchors. RESULTS Total, trabecular, and cortical bone mineral densities were an average of 50%, 50%, and 10% higher, respectively, in the proximal part of the tuberosities compared with the distal part (p < 0.01). Within the proximal part of the greater tuberosity, trabecular bone mineral density of the posterior region and cortical bone mineral density of the middle region were, on the average, 25% and 16% higher, respectively, than the densities in the other regions (p < 0.01). Load to failure in the proximal part of the tuberosities was an average of 53% higher than that in the distal part (p < 0.01). The lesser tuberosity showed, on the average, a 32% higher load to failure than did the greater tuberosity (p < 0.01). Within the proximal part of the greater tuberosity, loads to failure in the anterior and middle regions were, on the average, 62% higher than the load to failure in the posterior region (p < 0.01). Overall positive correlations were found between bone mineral density and load to failure (0.65 </= r </= 0.74, p < 0.01). CONCLUSIONS We found that pullout strength of suture anchors correlates well with bone mineral density of the tuberosities. Higher loads to failure were found in regions in the proximal part of the tuberosities. Placement of anchors in these regions may prevent anchor loosening, formation of a tendon-bone gap, and failure of the rotator cuff repair.

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.

Failure strengths in distal biceps tendon repair

Background Surgical repair is the most favored treatment for a rupture of the distal biceps tendon. A variety of techniques have been described for distal biceps tendon reattachment, including transosseous sutures, suture anchors, interference screws, and an EndoButton-based technique. Hypothesis EndoButton and suture anchor have initially stronger fixation strengths than do transosseous sutures, allowing early postoperative rehabilitation. Study Design Controlled laboratory study. Methods Single loads to failure and mode of failure of 13 different fixation techniques were determined using 130 human cadaveric elbows. Quantitative computer tomography was performed to exclude differences in bone mineral density as an affecting factor. Repeated-measures analysis of variance was used to assess differences in failure load between repair techniques. Results The EndoButton-based technique showed a significantly higher failure load (259 ± 28 N) than did all other techniques (P < .05). No significant differences were seen between the transosseous suture technique (210 ± 29 N) and most other techniques (P > .05). Failure loads of the TwinFix-QuickT (57 ± 29 N) and Biocuff screw (105 ± 28 N) were significantly lower than those of all other repairs (P < .05). Conclusion Significant differences exist in failure loads and modes of failure for the different repair techniques after rupture of the distal biceps tendon. Clinical Relevance The transosseous technique is still a sufficient and cost-saving procedure for repair of the distal biceps tendon. TwinFix-QuickT 5.0 mm and Biocuff screw 5.7 mm had significantly lower failure loads, which might affect early rehabilitation, particularly in patients with poor bone quality.

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° varus and 3° 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.

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.

Magnetic resonance imaging in quantitative analysis of rotator cuff muscle volume.

Tears of the rotator cuff are accompanied by muscle atrophy, which has direct implications on patient outcome after rotator cuff surgery. However, no reliable method exists to determine muscle volumes in situ. The current authors evaluated the reliability of magnetic resonance imaging in assessing rotator cuff muscle volumes. Muscle volumes were determined in 10 shoulders from cadavers using two methods: (1) oblique sagittal shoulder scans were obtained, the contours of the supraspinatus, infraspinatus and teres minor, and subscapularis muscles were traced, and muscle volumes were calculated using image analysis software; and (2) rotator cuff muscles were dissected and muscle volumes were measured by water displacement. The average magnetic resonance imaging volume of the supraspinatus, infraspinatus and teres minor, and subscapularis muscles were 36 ± 12, 96 ± 41, and 99 ± 33 mL, respectively. There was a significant correlation between magnetic resonance imaging and water displacement measurements. The intraobserver and interobserver variabilities were less than 4%. The results indicate the magnetic resonance imaging is a reliable method to determine rotator cuff muscle volumes with good intraobserver and interobserver variability. This method may prove valuable preoperative assessment of rotator cuff muscles and prediction of outcome after rotator cuff repair.

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.