Total knee arthroplasty: posterior tibial slope influences the size but not the rotational alignment of the tibial component.

PURPOSE: The reasons leading to rotational tibial malalignment in total knee arthroplasties (TKAs) remain unclear. A previous cadaver study has shown an increase in internal rotation of the anatomical tibial axis (ATA) after the tibial cut. This study investigates the influence of tibial slope on the ATA and the size of the resected tibial surface. METHODS: CT scans of 20 cadaver knees were orientated in a standardized coordinate system and used to determine the position of the centres of rotation of the medial and lateral tibial articular surfaces and, hence, of the ATA, after a virtual resection of 6 mm with 0°, 3.5°, 7° and 10° slope, respectively. Furthermore, at each slope, the radii of the medial and lateral tibial articular surfaces after resection were calculated. RESULTS: Compared to resection of 6 mm with 0° slope, a slope of 3.5° resulted in a mean external rotation of the ATA of 0.9° (SD, 1.5°; P = 0.025). A slope of 7° resulted in a mean external rotation of the ATA of 1.0° (SD 2.0°; P = 0.030) and a slope of 10° had no influence on the rotation of the ATA. The radii of the medial and lateral articular surfaces of the cut tibiae were larger than those of the uncut tibia (P < 0.001). CONCLUSION: Differences in the posterior tibial slope should not contribute to a rotational malalignment when using the ATA to align the prosthetic tibial plateau. Although statistically significant, the change in ATA with increasing slope was negligible.

[Developments in hip arthroplasty]. / Entwicklungen in der Hüftendoprothetik.

Developments in hip arthroplasty Abstract. The principles of the hip arthroplasty, as we know them today, were established about 60 years ago by Sir John Charnley. Replacement of the hip joint became one of the most successful and safest therapeutic procedures. Hip arthroplasty has been shown to yield good long-term results without complications. Over the last 20 years, the development and establishment of minimally invasive operation techniques has contributed to rapid changes. Additionally, perioperative patient management was optimized. Improvements in the material and tribology of the implants led to promising developments. Nonetheless, analysis of possible complications, shows potential for further developments, for example in cup geometry. Enhanced training concepts for surgeons, operation simulators, simple navigation aids for component positioning can surely achieve improvements in surgical safety.

Using the anatomical tibial axis for total knee arthroplasty alignment may lead to an internal rotation error.

INTRODUCTION: Despite intensive research, current total knee arthroplasty (TKA) designs do not always provide the correct kinematics for the native joint and thus further optimisation is necessary. Several studies support the importance of malrotation of the tibial components in the failure of TKA. We hypothesise that using the anatomical tibial axis (ATA) to align tibial component rotation on the resected tibial surface may lead to an internal rotation error due to relative anterior shift of the lateral articular surface centre compared to the medial one. The aim of this study was to compare the anatomical tibial axis of the physiological tibial joint surface to the resected one. METHOD: Twenty formalin-fixed cadaveric knees were obtained for study. After computed tomography scanning the data of each specimen were entered into a standardised coordinate system and virtual bone cuts were performed with 6, 8 and 10 mm resection depths. The positions of the articular surface centres were determined at each resection depth. RESULTS: The lateral articular surface centre had moved anteriorly after the resection by a mean 1.475 mm, while the medial one had not changed significantly. Resecting the tibia at a 6-mm cut and using the transverse tibial axis to align the prosthetic tibial plateau will result in a mean 4.0° (95 % confidence interval, 2.5-5.5°) of internal rotation compared to the uncut tibia. DISCUSSION: The ATA lies in 6 degrees of external rotation compared to the perpendicular to the posterior tibial condylar axis (PTCA). Graw et al. suggest aligning the tibial component in 10 degrees of external rotation to the latter. Thus, if we accept the above suggestion, the ATA is 4 degrees internally rotated compared to the same line on the resected proximal tibia. These prior studies appear to be in accordance with our findings. CONCLUSIONS: We conclude that using the ATA on the resected tibial surface may contribute to an internal rotation error.

Influence of tibial slope on extension and flexion gaps in total knee arthroplasty: increasing the tibial slope affects both gaps.

PURPOSE: Increasing the tibial slope is often performed if the flexion gap is narrower than the extension gap. The main hypothesis of this study is that increasing the tibial slope coincidentally enlarges the extension gap. METHODS: Twenty formalin-fixed cadaveric knees were obtained for study. After CT in full extension and 90° flexion, the data of each specimen were entered into a standardized coordinate system and virtual bone cuts were performed with incrementally increasing the posterior slope. Gaps were measured at tibiofemoral contact points in 90°-flexion and full extension in the medial and lateral compartment. RESULTS: Increasing the tibial slope did significantly widen both the extension and the flexion gaps (p < 0.001). In extension, the opening rates, i.e. the gap increase per degree of slope increase, were equal medially and laterally (0.5 mm ±0.1) medial vs 0.6 mm (±0.0) lateral), whereas in flexion the lateral gap did open significantly more than the medial one (0.6 mm ±0.1) medial vs 0.9 mm (±0.1) lateral (p < 0.001), resulting in a significantly greater flexion gap laterally. CONCLUSIONS: Increasing the tibial slope beyond the pre-operative planning in order to widen a tight flexion gap intra-operatively is not recommended as doing so will increase the extension gap simultaneously and will make the medial and lateral flexion gaps unequal.

Micro CT analysis of the subarticular bone structure in the area of the talar trochlea.

PURPOSE: Certain regions of the talar trochlea are recognized as exhibiting varying cartilage thickness and degrees of subchondral bone mineralization. These changes have been attributed to the long-term loading history. For the current study, we accepted the hypothesis that stress-induced alterations of the joint surface include not only varying degrees of subchondral lamellar mineralization, but also structural changes of the subarticular cancellous bone. METHODS: In order to examine the structure of the subarticular cancellous bone, ten formalin-fixed talar trochleae were analyzed using micro CT. Sixteen measurement zones were defined and then evaluated in five layers each of 1-mm thickness, enabling assessment of the cancellous architecture extending 5 mm below the trochlear surface using numerical and structural parameters. RESULTS: As with mineralization patterns in the subchondral lamella, large variation was observed regarding bone volume, trabecular quantity, thickness, and spacing, as well as for structure model index and degree of anisotropy, depending on localization. In addition, like previous reports examining mineralization of the subchondral lamella, two distinct groups could be identified as "bicentric" or "monocentric". CONCLUSIONS: These results show that structural tissue adaptation probably due to loading history is also evident within the subarticular cancellous bone.

Computer tomographic evaluation of talar edge configuration for osteochondral graft transplantation.

To successfully surgically reconstruct osteochondral lesions of the talus, the exact three-dimensional (3D) configuration of the upper articular surface of the talus has to be respected. We assessed the talar geometry by measuring the coronal and sagittal talar edge radius and the frontal talar profile in multiplanar reconstructions of computer tomographic (CT) studies of 79 patients (83 feet) with a healthy ankle joint. An image visualization software designated for coordinate measurement was used to perform the measurement. In the coronal plane, the mean lateral talar edge radius was 4.0 mm and the medial 4.5 mm. In the sagittal planes the mean lateral talar edge radius was 20.3 mm, the radius of the sulcus 20.7 mm and the medial talar edge radius 20.4 mm. The talus showed a concave shape in coronal cuts. These results show a significant difference between medial and lateral talar edge configuration in coronal planes. The measurements of the lateral and medial sagittal radius and the mid-sagittal radius in the sulcus tali show no statistically significant difference. The depth of the talar sulcus shows no correlation to age or sex. Different sizes of custom-made tissue-engineered grafts according to the location of the osteochondral lesion at the talus are needed for exact surgical reconstruction of the anatomy. Osteochondral lesions are three dimensional; therefore, a 3D preoperative planning tool by CT scan or MRI is mandatory.

Development of a force-determining tensor to measure "physiologic knee ligament gaps" without bone resection using a total knee arthroplasty approach.

BACKGROUND: Ligament balancing is a challenging but essential part of successful total knee arthroplasty. There is general agreement that flexion and extension gaps should be equal and symmetrical. However, to date there are no available comparisons to physiologically normal knee joints that have not undergone bone resection. There are also no standards specifying which instruments (e.g., spacers, distractors, trial components, navigation systems) and particularly what degree of force should be used for gap distraction. METHODS: To measure the physiological extension and flexion gaps, a prototypical force-determining tensor (Aesculap, Tuttlingen, Germany) was constructed and adapted so that force could be applied directly through Schanz screws inserted medially and laterally on the tibia and femur, independent of each other and without the need for bony resection. Ten normal cadaveric knees were assessed using a standard medial parapatellar total knee arthroplasty approach with patellar subluxation. Gap measurements were carried out twice, alternating distraction forces of 100 and 200 N each time. RESULTS: The prototype was implemented successfully. Repeat measurements showed only slight deviation from the original, resulting in minimal standard error. Precision did not vary with the application of greater force (200 N), but gap size increased significantly (p < 0.001). CONCLUSIONS: The success of this assessment with cadaveric knees indicates that this prototype can be applied to measure flexion and extension gaps without the need for bony resection. Increasing the distraction force to 200 N does not improve results, so 100 N per compartment appears adequate. Most likely, the extension and flexion gaps are physiologically asymmetric and unequal, and the kinematics are markedly altered after resection of the PCL and/or ACL. This new force-determining tensor can be used for further analyses, e.g., to explore the effects of selective ligament resection.

A biomechanical comparison of two plating techniques in lateral clavicle fractures.

BACKGROUND: Neer Type IIb lateral clavicle fractures typically lead to dislocation of the medial fragment. Therefore, most surgeons recommend surgical treatment for such a fracture pattern. The use of a locking compression plate with a lateral extension has produced satisfactory results in various studies over recent years. Double-plate fixation is a common technique in the treatment of complex distal radius fractures. The authors use this technique as a routine procedure in the treatment of Neer type IIb fractures. In this biomechanical testing study, the mechanical properties of the two techniques were compared. METHODS: On 20 clavicles from fresh frozen cadavers a Neer Type IIb fracture-like osteotomy was performed. A cyclic loading test followed by a load-to-failure test was carried out. Parameters for statistical evaluation were the stiffness at cycles 1, 100 and 17,500 as well as the ultimate tensile load and the deformation at the point of failure. FINDINGS: All specimens withstood the cyclic loading test without any noticeable damage. At cycles 100 and 17,500, the double-plate technique was less stiff. Failure loads were not significantly different from each other, but deformation at the point of failure was significantly greater for the double-plate technique. INTERPRETATION: Both techniques provided sufficient fixation to the fracture site to endure the cyclic loading test, which is supposed to simulate an incident-free week postoperatively. In summary, the double-plate technique offers biomechanically a feasible alternative to the single-plate technique in lateral clavicle fractures of Neer Type IIb.

The glenohumeral joint - a mismatching system? A morphological analysis of the cartilaginous and osseous curvature of the humeral head and the glenoid cavity.

BACKGROUND: Radial mismatch, glenohumeral conformity ratios and differences between cartilaginous and osseous radii highly depend on the measured plane. The comparison of cartilaginous radii between humeral head and glenoid in different planes provides new information to understand the degree of conformity during abduction of the upper limb. METHODS: To investigate the radii, CT-images in soft-tissue kernel of 9 specimen were analysed using an image visualization software. Statistical analysis of the obtained data was performed using the t-test. RESULTS: Measurements of the radii in the glenoid revealed a significantly larger radius for bone than cartilage, whereas for the humeral head the opposite was the case. Highest ratios for cartilage in the transverse plane were found in the inferior and central areas of the joint surface, whereas the smallest ratios were found in the superior area. The radial mismatch varied between 0.1 mm and 13.6 mm, depending on the measured plane. CONCLUSIONS: The results suggest that in abduction, the cartilaginous guidance of the humeral head decreases. This might permit the humeral head an anterior-posterior shifting as well as superior-inferior translation. Surgical reconstruction of the normal glenohumeral relationships necessitates precise information about the glenohumeral morphology to ensure proper sizing and correct placement of prosthetic components and osteochondral allografts.

Retrograde synovial biopsy of the knee joint using a novel biopsy forceps.

Synovial biopsies of the knee joint are commonly performed arthroscopically with the patient under full or regional anesthesia. To overcome the effort, costs, and potential risks of surgery, we developed an office-based technique for retrograde synovial biopsy using a designated novel biopsy forceps. Using this technique, no arthroscopic or radiologic control is needed to perform rapid synovial biopsies of the knee joint. Concomitant aspiration of synovial fluid can be performed. A technical description of the procedure is given.

Novel polyvinyl alcohol (PVA) based cryoprotection method that facilitates cutting frozen sections of decalcified human trabecular bone.

Processing adult human trabecular bone to obtain tissue sections suitable for research or diagnostic purposes has always been challenging, particularly in the preparation of adult bone specimens for advanced immunohistochemistry applications. In contrast to the majority of soft tissues, decalcified bone samples perform poorly under standard paraffin embedding techniques and immunolabeling protocols fail frequently, due to the loss of protein antigenicity observed. We report on a new, PVA based infiltration method that avoids excessive heat exposure to tissue samples during embedding. The developed PVA based infiltration medium provides sufficient structural support to the heterogenic morphology and distinct architecture of subchondral trabecular bone and adjacent articular cartilage. Furthermore, the addition of bovine serum albumin (BSA) to this infiltration solution guaranteed safe attachment of cryosections to glass slides. The protocol allows the preparation of high quality sections of adult human trabecular bone tissues which can be used for both classical histochemical stains and for immunohistochemistry, since protein antigenicity is satisfactorily preserved.

Measurement of knee joint gaps without bone resection: "physiologic" extension and flexion gaps in total knee arthroplasty are asymmetric and unequal and anterior and posterior cruciate ligament resections produce different gap changes.

General agreement is that flexion and extension gaps should be equal and symmetrical in total knee arthroplasty (TKA) procedures. However, comparisons using a standard TKA approach to normal knee joints that have not undergone bone resection are currently unavailable. Since bony preparation can influence capsule and ligament tension, our purpose was to perform measurements without this influence. Ten normal cadaveric knees were assessed using a standard medial parapatellar TKA approach with patellar subluxation. Gap measurements were carried out twice each alternating 100 and 200 N per compartment using a prototypical force-determining ligament balancer without the need for bony resection. Initial measurements were performed in extension, followed by 908 of flexion. The ACL was then resected, and finally the PCL was resected, and measurements were carried out in an analogous fashion. In general, the lateral compartment could be stretched further than the medial compartment, and the corresponding flexion gap values were significantly larger. ACL resection predominantly increased extension gaps, while PCL resection increased flexion gaps. Distraction force of 100 N per compartment appeared adequate; increasing to 200 N did not improve the results.