Usefulness of the "grand-piano sign" for determining femoral rotational alignment in total knee arthroplasty

"Boot Sign" of Anterior Femoral Condylar Resectional Shape during Total Knee Arthroplasty Is More Frequent in Asian Patients

PURPOSE

There is lack of intraoperative consensus on the distal femur anterior resected surface shape that allows reliable rotational alignment assessment during total knee arthroplasty (TKA). We aimed to evaluate the ratio and prevalence of anterior femoral resection surface intraoperatively.

MATERIALS AND METHODS

The study included 234 osteoarthritis patients with varus knees and not valgus knees or deformities. After conventional medial parapatellar approach, measured resection technique based on the mechanical axis of the femur and preoperative TEA-PCA angle on CT with anterior reference was used among all the patients. The anteroposterior (AP) lengths after distal femoral resection were measured as the femoral lateral AP (FLAP) and femoral medial AP (FMAP) lengths. Based on the medial (MD) and lateral condyle (LD) vertical distance ratios of the femur anterior resected surface, the groups were classified into "boot sign", "grand-piano", and "butterfly sign" groups. For comparison of the mean values, the data were assessed for normality with the Shapiro-Wilk test. One-way ANOVA with post hoc analysis using Tukey's honestly significant difference (HSD) test was used to compare the mean values among the groups. The correlations between the MD/LD and variables were analyzed using the Pearson correlation coefficient. Linear regression analyses were used to find the associated factors to the anterior femoral resection surface shape.

RESULTS

Mean intraoperative femoral rotation and distal femoral cutting angles were 4.9° ± 1.2 and valgus 5.0° ± 0.7, respectively. Mean FLAP was 52.9 ± 4.2 mm. Mean MD/LD (0.61 ± 0.13) was lower than that of typical "grand-piano sign". The morphological shape incidence of the "boot sign" was 62.4%. In the "boot sign" group, the FLAP was found to be smaller than that in the other groups (52.4 ± 4.2 vs. 53.7 ± 4.2 vs. 54.9 ± 2.7; p = 0.02), while the intraoperative femoral rotation angle was found to be larger than in the other groups (5.0 ± 1.2 vs. 4.6 ± 1.1 vs. 4.7 ± 1.2; p = 0.039). The MD/LD-associated factors were FLAP, intraoperative femoral rotation, and distal femoral cutting angles (R2 = 0.268).

CONCLUSION

The femur anterior resection surface shape in TKA was found in the "boot sign" rather than the "grand-piano sign" in Korean ethnics owing to an asymmetric morphology of femoral condyles. Ethnic differences, including distal femoral morphology, should be considered for assessment of the femoral rotation angle using the femur anterior resection surface shape.

"Grand-piano sign" as a femoral rotational indicator in both varus and valgus knees: a simulation study of anterior resection surface in total knee arthroplasty

PURPOSE

The "Grand-piano sign" is a popular indicator of the appropriate rotational alignment of the femoral component during total knee arthroplasty (TKA). The aim of the study was to investigate the shape of the anterior femoral resection surface of varus and valgus knees.

METHODS

A cohort of 80 varus knees and 40 valgus knees (hip-knee-ankle angle > 2° for varus and < - 2° for valgus knees) matched for age, sex, height, body weight, and KL grade was made using propensity score matching. Virtual TKA was performed using 3 patterns of components (anterior flange flexion angles of 3°, 5°, and 7°). The anterior femoral resection surface was evaluated for 3 patterns of rotational alignments: parallel to the surgical epicondylar axis (NR, neutral rotation), 3° internal rotation (IR), and 3°external rotation (ER) relative to the surgical epicondylar axis. In each anterior femoral resection surface, the vertical height of medial and lateral condyles was measured, and the ratio of the medial to the lateral height (M/L ratio) was evaluated.

RESULTS

The M/L ratio in NR for both varus and valgus knees was 0.57 to 0.64, with no significant difference between the cohorts (p value > 0.05). The M/L ratio showed a similar pattern of increasing at IR and decreasing at ER in both varus and valgus knees. The variation in the M/L ratio with malrotation in valgus knees was smaller than in varus knees.

CONCLUSION

During TKA, the anterior femoral resection surface was similar in varus and valgus knees; however, the variation with malrotation was smaller in valgus knees than in varus knees. TKA for valgus knees requires precise surgical technique and careful intraoperative assessment.

LEVEL OF EVIDENCE

IV, Case series.

Importance of Three-Dimensional Evaluation of Surgical Transepicondylar Axis in Total Knee Arthroplasty

In total knee arthroplasty, the surgical transepicondylar axis (SEA) is one of the most reliable rotation axes for stabilizing of the patellofemoral joint. The SEA is identified with reference to the lateral epicondyle and the medial sulcus of the medial epicondyle. However, these two structures rarely appear on the same plane on computed tomography (CT), and it is necessary to take two points in separate images. Many surgeons measure the SEA on the same image (pseudo SEA) instead. We aimed to determine the difference between true SEAs and pseudo SEAs. A total of 31 normal knees and 24 varus knees were included in this study. Three-dimensional (3D) models of the femur were reconstructed from CT images, and a reconstructed plane was made using the International Society of Biomechanics coordinate system. Pseudo SEAs drawn in the plane passing through the lateral epicondyle and medial sulcus were defined as l-SEA and m-SEA, respectively. L-SEA, m-SEA, true SEA, and posterior condylar axis (PCA) were projected onto the International Society of Biomechanics coordinate plane and, "p l-SEA," "p m-SEA," "p true SEA," and "p PCA" were obtained. The true SEA angle was defined as the angle between p true SEA and p PCA. The l-SEA angle or m-SEA angle was defined as the angle between the p l-SEA or p m-SEA and p PCA, respectively. There were no statistically significant differences between true SEA angle (2.64 ± 2.01 degrees) and pseudo SEA angle (l-SEA angle: 2.74 ± 2.07 degrees, m-SEA: 2.54 ± 2.19 degrees). Conversely, 12 knees in the normal group and 2 knees in the varus group had differences of more than 1 degree (p = 0.01). Among them, 6 knees in the normal group and 0 knees in the varus group had a difference of 2 degrees or more (p = 0.03). In most cases, pseudo SEA can be substituted for true SEA.

Visual Illusions in Radiology: Untrue Perceptions in Medical Images and Their Implications for Diagnostic Accuracy

Errors in radiologic interpretation are largely the result of failures of perception. This remains true despite the increasing use of computer-aided detection and diagnosis. We surveyed the literature on visual illusions during the viewing of radiologic images. Misperception of anatomical structures is a potential cause of error that can lead to patient harm if disease is seen when none is present. However, visual illusions can also help enhance the ability of radiologists to detect and characterize abnormalities. Indeed, radiologists have learned to exploit certain perceptual biases in diagnostic findings and as training tools. We propose that further detailed study of radiologic illusions would help clarify the mechanisms underlying radiologic performance and provide additional heuristics to improve radiologist training and reduce medical error.

Change in leg length after open-wedge high tibial osteotomy can be predicted from the opening width: A three-dimensional analysis

BACKGROUND

The purpose of this study was to evaluate true change in leg length after open-wedge high tibial osteotomy (OWHTO) using three-dimensional (3D) assessments, examine the factors that influence leg lengthening and verify their validity in clinical practice.

METHODS

Study 1: a retrospective case series simulation study, included 46 patients (55 knees) that underwent knee arthroplasty or HTO. OWHTO was simulated from preoperative computed tomography using 3D preoperative planning software. Uni- and multivariate regression analyses were conducted to identify predictors related to change in leg length. Study 2: a retrospective case series study, included 53 patients (55 knees) that underwent OWHTO in another institution. Change in leg length was measured preoperatively and 1 year postoperatively and was compared with the predicted change in leg length calculated using the formula obtained from Study 1.

RESULTS

Study 1: the true change in leg length significantly increased and showed a strong correlation with the opening width. The change in leg length was predicted using the formula "change in leg length = opening width × 0.75-1.5." Study 2: the predicted change in leg length showed no significant difference from the change in leg length 1 year postoperatively and a strong correlation with the measured change.

CONCLUSIONS

The true change in leg length after OWHTO was predicted using the formula obtained from the 3D model. Predicting the change in leg length preoperatively can be a basis to consider other HTOs.

Intra- and postoperative assessment of femoral component rotation in total knee arthroplasty: an EKA knee expert group clinical review

PURPOSE

Malrotation of the femoral component after primary total knee arthroplasty (TKA) is one of the most important problems leading to painful TKA requiring revision surgery.

METHODS

A comprehensive systematic review of the literature was performed to present current evidence on how to optimally place the femoral component in TKA. Several landmarks and techniques for intraoperative determination of femoral component placement and examination of their reliability were analyzed.

RESULTS

2806 articles were identified and 21 met the inclusion criteria. As there is no unquestioned gold standard, numerous approaches are possible which come along with specific advantages and disadvantages. In addition, imaging modalities and measurements regarding postoperative femoral component rotation were also investigated. Femoral component rotation measurements on three-dimensional (3D) reconstructed computerised tomography (CT) images displayed intraclass correlation coefficients (ICC) above 0.85, significantly better than those performed in radiographics or two-dimensional (2D) CT images. Thus, 3D CT images to accurately evaluate the femoral prosthetic component rotation are recommended, especially in unsatisfied patients after TKA.

CONCLUSION

The EKA Femoral Rotation Focus Group has not identified a single best reference method to determine femoral component rotation, but surgeons mostly prefer the measured resection technique using at least two landmarks for cross-checking the rotation.

LEVEL OF EVIDENCE

III.

Revision arthroplasty with rotating hinge systems for total knee arthroplasty instability

OBJECTIVE

Restoring stability after total knee arthroplasty (TKA) and improving joint function using a cemented rotating hinge system.

INDICATIONS

Ligament instability and/or osseous defects (including Anderson Orthopaedic Research Institute [AORI] classification type II defects) after primary TKA or TKA revision surgery.

CONTRAINDICATIONS

Distal femoral or proximal tibial bowing requiring implant systems that provide femoral or tibial offset stems. Persistent periprosthetic infection. Poor therapeutic compliance. AORI type III defects.

SURGICAL TECHNIQUE

Medial arthrotomy. Femoral and tibial component removal with small saw blades and chisels. Intramedullary alignment for the tibial and femoral cuts. Debridement and removal of membranes and cement remnants. Reconstruction of joint line and correct TKA alignment. Trial reduction. Cement fixation.

POSTOPERATIVE MANAGEMENT

Unrestricted range of motion, partial weight bearing for 4 weeks.

RESULTS

Between 2012 and 2013, 18 patients suffering from ligament insufficiency after TKA were revised using the described system and included in a prospective study protocol. The mean follow-up was 37 months (range 30-46 months). There was a significant improvement of the Oxford Knee Score (OKS) from 19 (range 7-29) preoperatively to 29 (range 10-45) postoperatively (p = 0.004). The Knee Society Score (KSS) knee assessment subscore improved from 35 (range 9-70) to 67 (range 35-97) (p = 0.002) and the pain score from 7 (range 0-50) to 24 (range 0-50) (p = 0.008).

Revision of unicompartmental knee arthroplasty using the in situ referencing technique

OBJECTIVE

Revision of unicompartmental knee arthroplasty (UKA) to total knee arthroplasty (TKA) with the in situ referencing technique aiming to preserve as much ligament function and epi-metaphyseal bone stock as possible.

INDICATIONS

Aseptic loosening, progression of osteoarthritis, periprosthetic fracture, periprosthetic infection, arthrofibrosis, polyethylene wear, malalignment, instability, femoro-tibial impingement.

CONTRAINDICATIONS

Unexplained pain, localized or systemic active infection (anywhere).

SURGICAL TECHNIQUE

Referencing for the tibia and the femur cuts is performed prior to implant removal. The tibial cutting jig and the initial tibial resection level is set in a way that the sawblade just fits under the tibial implant. In case too much bone needs to be removed to achieve flush implant sitting on both the medial and lateral tibia, a step cut needs to be performed to build up the medial defect with an augment. Prior to femoral component removal, rotational alignment is determined and intramedullary referencing for the distal femur osteotomy is performed. Level of constraint and additional tibial stem fixation is chosen according to the amount of bone resected and according to ligament stability.

POSTOPERATIVE MANAGEMENT

Sterile dressings and elastic compression bandaging. No limitation of active/passive range of motion. Full weight-bearing or partial weight-bearing for 2 weeks postoperatively in the presence of bone or soft tissue defects.

RESULTS

Between 2008 and 2019, 84 patients underwent revision of unicompartmental knee arthroplasty. The mean follow-up was 64 months (range 3-132 months). Implant survival after revision of UKA to TKA was 92% (95% CI = 82-97%) at 5 years of follow-up and 86% (95% CI = 69-93%) at 10 years of follow-up. The mean Oxford knee score was 20.1 (6-39, SD ± 6.5) preoperatively and 30.2 (3-48, SD ± 11.3) postoperatively. The mean visual analogue scale was 6.9 (range 1-10, SD ± 1.8) preoperatively and 3.9 (range 0-9, SD ± 2.6) postoperatively.