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.

Comparison of knee joint orientation in clinically versus biomechanically aligned computed tomography coordinate system

Background

Preoperative planning of total knee arthroplasty is usually performed using knee-centred computed tomography (CT) data sets. The disadvantage of these data sets is having no account of the biomechanical axis of the lower extremity, known as Mikulicz line. It aligns the femoral head to the middle of the talocrural joint. For optimal prosthesis arrangement, the knee CT data set must therefore be brought in congruency with this line of loading to achieve the best results and eliminate rotational malalignments.

This study aims to establish a relation between the knee-centred clinical coordinate system (CCS) and a biomechanical coordinate system (BCS) based on the Mikulicz line.

Methods

CT data sets of 45 lower extremities were evaluated. Using VG Studio Max, a visualisation and measurement software program; each CT data set was aligned according to the CCS and BCS. After superimposing both the aligned data sets, the deviations of both coordinate systems in all three planes were measured with the centre of the knee defined as the origin.

Results

For the coronal plane, the CCS was demonstrated to be 2.54° in adduction compared to the BCS [standard deviation (SD) = 1.8°]. In sagittal view, the CCS was demonstrated to be 0.3° retroversed (SD = 3.27°). Finally, the deviation in the axial plane showed an outward rotation of 3.39° (SD = 1.99°). The alignment as well as the measurements demonstrated high intraobserver and interobserver reproducibility.

Conclusion

Both coordinate systems can be established in knee-centred CT data sets in a reproducible manner. Clearly, the CCS differs significantly from the BCS describing the biomechanical axis, but mathematical-based adaptations and corrections can be performed.

The translational potential of this article

The findings of this study allow a mathematical conversion of a knee CT to the biomechanical axis of the leg.

Intraprosthetic dislocation of dual mobility total hip arthroplasty: still occurring?

PURPOSE

The objective was to identify predictive factors for intraprosthetic dislocation (IPD) and to understand how improvements in dual mobility cups (DMC) have helped to reduce dramatically the occurrence of this complication.

METHODS

DM mobile inserts retrieved from 93 hips were divided into three groups: first-generation DMC with IPD ("firstDMC-IPD"), first-generation DMC with over 15 years of implantation without IPD ("firstDMC-noIPD"), and latest-generation DMC ("newDMC"). The predictive factors for IPD based on clinical, prosthetic, radiological and intraoperative characteristics were analysed by multivariate analysis. The surface of each retrieved mobile insert was analysed using three-dimensional CT scan in order to compare their rim wear.

RESULTS

Three predictive factors for IPD were found: a high BMI, a wide rough stem neck and a large cup size. Wear of the firstDMC-noIPD inserts was significantly less than those of firstDMC-IPD inserts and significantly more than those of newDMC inserts. For the firstDMC-IPD inserts, the rim's outer surface wear was significantly greater than the rim's inner surface wear.

CONCLUSIONS

IPD is a specific complication related to wear of the DM mobile insert due to failure of the liner's retaining rim, especially from the rim's outer surface. This long-term issue is different to the early traumatic complication, which can happen after an attempt at closed reduction of a DM THA dislocation. Recent modifications in the design and the coating of contemporary DMC and femoral stems, as well as improvements in the mobile insert itself, seem to corroborate our assumptions about the IPD mechanism and contribute to the quasi-disappearance of this complication.

Computed Tomographic Evaluation of Joint Geometry in Patients With End-Stage Ankle Osteoarthritis

BACKGROUND

Deformation of the talus and the distal tibia can be frequently observed during ankle joint osteoarthritis (OA). The aim of this study was to objectify these morphologic changes. We hypothesized that a flattening of the talus and a broadening of the distal tibia surface occurs in end-stage OA of the ankle joint.

METHODS

Twenty-seven computed tomography (CT) ankle joint examinations of unilateral ankle OA were matched by sex and age with 27 CT examinations of healthy ankle joints. Three-dimensional reformatting and measurements were performed with geometry analysis software. The following parameters were assessed: sagittal radius of the talus, talus height, and mediolateral and anteroposterior width of the distal tibial joint surface.

RESULTS

Medial, midsagittal, and lateral sagittal arc radii of osteoarthritic tali were significantly larger compared to tali of controls. There was a statistically significant difference in the height of the osteoarthritic talar dome in the medial and in the lateral frontal segment and in the medial central segment compared to tali of controls. The anteroposterior width and the sagittal curvature of the distal tibia was significantly larger in OA ankles than in the control group. The mediolateral measurements were comparable across both groups.

CONCLUSION

Flattening of the talus appears to be more pronounced in the frontal aspect of the talus. The distal tibia broadens anteroposteriorly. These findings may contribute to better understanding of ankle OA development.

LEVEL OF EVIDENCE

Level III, retrospective comparative cohort study.

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.

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.

Glenohumeral relationships: subchondral mineralization patterns, thickness of cartilage, and radii of curvature

Subchondral mineralization represents the loading history of a joint and can be measured in vivo using computed tomography osteoabsorptiometry. Different mineralization patterns in the glenohumeral joint have been explained by the principle of physiologic incongruence. We sought to support this explanation by measurement of mineralization, radii, and cartilage thickness in 18 fresh shoulder specimens. We found three mineralization patterns: bicentric, monocentric anterior, and monocentric central. Mean radii of the glenoids were 27.4 mm for bicentric glenoids, 27.3 mm for monocentric anterior, and 24.8 mm for monocentric central glenoids. Cartilage thickness measurement revealed the highest values in anterior parts; the thinnest cartilage was found centrally. Our findings support the principle of a physiologic incongruence in the glenohumeral joint. Bicentric mineralization patterns exist in joints consisting of more flat glenoids compared to the corresponding humeral head. Monocentric distribution with a central maximum was found in specimens with glenoids being more curved, indicating higher degrees of congruence, which might represent an early stage of degenerative disease. The obtained information might also be important for implant fixation in resurfacing procedures or to achieve the best possible fit of an osteochondral allograft in the repair of cartilage defects.