The Trochlear Paradox in Native Knees and Its Potential Impact on Total Knee Arthroplasty: An MRI-Based Correlation Study Investigating the Effect of Varying Posterior Femoral Condyle Angles on the Patellofemoral Joint.

BACKGROUND: Since the beginning of total knee arthroplasty, implant alignment has been a central point of discussion. As diverse as the discussed alignment theories are, as uniform is the implant design, which is supposed to be based on the "average knee." Steady upgrades in prosthesis design and modern alignment theories have achieved improvements. However, knee arthroplasty continues to be burdened by a significant percentage of dissatisfied patients. In current knee arthroplasty, femoral implant alignment is referenced by the dorsal and distal condylar axes. The patellofemoral joint variance is not sufficiently considered. Predominantly dorsal and distal referencing at the femoral condyle determines the postoperative shape of the anterior knee joint. The present study investigated a possible relationship between dorsal and distal joint parameters and the patellofemoral joint. METHODS: In this explorative retrospective monocentric study, MRI cross-sectional images of 100 native knee joints were evaluated. By determining parametric correlations according to Pearson, the study investigates whether the independent variables "posterior femoral condyle angle" and "lateral distal femoral angle" are related to "lateral trochlear inclination", "patella tilt", and "bisect offset". RESULTS: The posterior condylar angle significantly correlates with lateral trochlear inclination, patella tilt, and bisect offset. There is a positive correlation with patella tilt and bisect offset but a negative correlation with lateral trochlear inclination. The lateral distal femoral angle did not correlate with the studied parameters. CONCLUSION: The lateral trochlear inclination decreases with an increased posterior femoral condylar angle. The posterior referencing of the femoral component in total knee arthroplasty simultaneously establishes the shape of the anterior knee joint. Our results indicate that increasing posterior condyle angles significantly correlate with flattened lateral trochlear inclinations in native knees and suggest a systematic biomechanical conflict in total knee arthroplasty.

Clinical effects of different center of rotation reconstructions in total hip arthroplasty after femoral neck fractures: a cohort study including a follow-up analysis on patient's mobility and daily living ability.

BACKGROUND: The aim of this study is a clinical evaluation of the center of rotation (COR) placement towards a patient's recovery with respect to daily living ability and mobility. In past experiments based on three-dimensional (3D) models, medialization of the COR in total hip arthroplasty (THA) showed a negative influence on muscle strength of the abductors and reaction force of the hip joint. This contradicts paradigms, where reduced hip loading forces are claimed to increase functional outcomes. METHODS: The plain X-rays of 110 patients who underwent THA after a femoral neck fracture between January 2019 and January 2021 were retrospectively evaluated. A Barthel Index on discharge was obtained in 69 cases. 47 patients were available for a follow-up interview concerning the Barthel Index, Parker mobility score (PMS), and pain levels (NRS) 6 and 12 months after surgery. RESULTS: Medialization of the COR had a significantly negative effect on the need for care (Barthel Index) at patient discharge (Spearman correlation 0.357, p = 0.013). The effect on the PMS is still existent at 6 and 12 months (Spearman correlation 0.471, p = 0.009 at 6 months; 0.472, p = 0.008 at 12 months). Mann-Whitney U tests showed that the groups with medialized COR performed significantly worse than the lateralized groups. This was seen for the Barthel Index at discharge and at 6 months after surgery and for the PMS at 6 and 12 months. The accurately reconstructed CORs showed no significant differences from the lateralized rotation centers in need of care and mobility. The superior COR placement group showed significantly reduced mobility at 12 months in contrast to the inferior COR placement group (p = 0.008), and the group of accurately reconstructed rotation centers showed significantly less pain than the inferior COR placement group (p = 0.007 after 6 months, p = 0.026 after 12 months). Especially the combination of both (superomedialization) leads to reduced mobility (Spearman correlation 0.67, p = < 0.001). CONCLUSIONS: COR superior displacement, COR medialization, and the combination of both (superomedialization, Spearman p = < 0.001) lead to reduced mobility while inferior displacement showed increased pain. According to our results, we recommend an exact vertical COR restoration, while horizontal medial displacement needs to be avoided. LEVEL OF EVIDENCE: III.

The Anterior Impingement After Mobile-Bearing Unicomparimental Knee Arthroplasty-A Neglected Problem. A Clinical Report of 14 Cases.

Background: Mobile-bearing unicompartmental knee arthroplasty (MB-UKA) is a proven implant that has reliably delivered excellent results for decades. Based on the constrained implant design in MB-UKA, the occasional occurrence of anterior impingement should be expected. However, surprisingly, there are no clinical reports. Methods: From 2016 to 2020, 14 patients with anterior medial knee pain were admitted to our arthroplasty center after MB-UKA implantation elsewhere. After taking the medical history and clinical examination, radiological imaging of the implant in at least 2 planes, including a whole-leg anteroposterior view, was performed. The "Knee Society Score (KSS)" and the "Knee Injury and Osteoarthritis Outcome Score (KOOS)" were recorded. Anterior impingement was diagnosed by reviewing the typical findings and specific exclusion of other diagnoses. Results: The 14 patients showed a KSS of 46.6 and a KOOS of 51.5. The average pain level on the "Visual Analog Scale" was 7.8. The positioning of the implants showed consistently noticeable deviations from the standard recommendations. All 14 patients were treated by removing the MB-UKA and changing to a complete TKA. At the 12-month follow-up, the average Visual Analog Scale score was 1.8, and KOOS and KSS were 86 and 82, respectively. Conclusions: The potential risk of anterior impingement in MB-UKA can be assumed. Diagnosis requires a detailed collection of medical history and clinical details combined with accurate radiological imaging. The cause of anterior impingement in MB-UKA is multifactorial and refers in our small group to the sum of minor deviations in implant positioning compared to the general recommendations.

A patient-specific 3D model of the knee to compare the femoral rollback before and after total knee arthroplasty (TKA).

PURPOSE: Total knee arthroplasty (TKA) is nowadays performed as a standard procedure on a large number of patients suffering from arthrosis. Replacing the knee joint causes changes in the geometry and kinematics of the knee, which are unique to each individual. This research focuses on the method to detect these changes after TKA and on the impact on the knee movement. This approach could reduce complications in patients with post-operative pain and reduce the number of revisions. METHODS: A 3D model of a patient's knee was made by measuring the movement with a medically certified infrared stereo camera. This measurement was combined with the 3D model of the patient's bones, previously segmented from the CT scan. This model is printed in 3D, one part being the mechanism that follows the movement of the patient, and the other part being the 3D copy of the femur and tibia bones. The knee replacement operation is performed directly on the model and the resulting rollback is being measured before and after TKA. RESULTS: We observe a difference in the rollback before and after TKA on the 3D printed model. The variation in size and shape of the femoral implant compared to the natural femur condyles is one of the reasons for the changes in the rollback effect. The rollback is half as large after the prosthesis insertion, which confirms the fact that the femoral prosthesis geometry influences the knee kinematics. CONCLUSIONS: In this study, a first 3D model combining the patient-specific kinematic and the geometry of his bones has been constructed. This model allows the surgeon to validate the plan of the operation, but also to understand the problems and consequences generated by the prosthesis insertion. The rollback is one of the most important motion of the knee joint and this behavior could be quantified, providing comparative analysis of the knee joint before and after the operation. As a future study, the model could be used to analyse more parameters of the TKA such as the impact of different implantation methods.

Advantages and disadvantages of 3D printing for pre-operative planning of revision hip surgery.

Total hip arthroplasty (THA) is one of the most successful and cost-effective interventions in medicine nowadays, providing reliable pain relief and functional improvement to those with osteoarthritis or inflammatory arthritis of the hip (P Kinov, B Antonov,'Possibilities for surgical treatment of acetabular osteolysis subsequent to revision arthroplasty of hip joint', Orthop Trauma. 52, 2015). Revision hip arthroplasty or severe reconstructive procedures in cases with significant anatomical defects require skilled surgical staff and accurate preoperative planning, including bone insufficiency, deficiency, discontinuity (anatomical assessment) as well as augmentation, cage or other requirements. (implant planning). Some authors recommend preoperative 3D model planning for precise anatomical assessment and preoperative training. This method has some limitations but could be successfully used in addition to conventional surgery.

[Minimally invasive anterolateral approach for total hip replacement (OCM technique)]. / Minimalinvasiver Zugang zum Hüftgelenk (OCM) zur Implantation von Hüftendoprothesen.

OBJECTIVE: Hip replacement with reduction of operative trauma. Thereby earlier mobilization and faster rehabilitation time compared with conventional techniques. No restrictions with regard to exposure of femur and acetabulum. INDICATIONS: Primary total hip arthroplasty. With experience also applicable in revisions. CONTRAINDICATIONS: None. SURGICAL TECHNIQUE: Patient in lateral position with fixed pelvis. Leg support for the leg being operated and modified leg support for the contralateral side on the operating table. Special retractors and instruments are advisable. Skin incision over the anterior portion of the greater trochanter slightly curved then over the muscular interval between gluteus medius and tensor fasciae latae. Fascia incision. Preparation of anterolateral muscular interval. Exposure and incision of capsule. Leg positioning for neck osteotomy in external rotation and hyperextension. For preparation of acetabulum leg again on support. Preparation of acetabulum and cup implantation. For femoral preparation leg in external rotation, hyperextension, and adduction. Capsular release nearby greater trochanter. Capsular release and stem implantation. Repositioning. Capsule and wound closure. POSTOPERATIVE MANAGEMENT: Early mobilization. Physical therapy and lymph drainage. Loading of the leg according to tolerance; if patient is pain-free, full weight bearing allowed. Thrombosis prophylaxis for at least 3 weeks postoperatively. RESULTS: Currently, the experience comprises over 3,500 patients operated on using the minimally invasive anterolateral approach since March 2003. Restrictions regarding indications are not known. In experienced hands, the technique can even be used for revision surgery. The clinical results show significant differences with improved clinical results as compared to patients after standard approaches, especially in terms of skin-to-skin time, blood loss, use of analgesics, rehabilitation time, and functional outcome. The accuracy of implant placement is not compromised. After a fundamental learning curve, there is no evidence of increased complications.

Anterolateral mini-incision hip replacement surgery: a modified Watson-Jones approach.

Mini-incision total hip replacement seeks to eliminate some complications of traditional extensile exposure and also attempts to facilitate more rapid rehabilitation of patients after surgery. Different surgical approaches historically have been used to do hip replacement surgery. Anterior or anterolateral approaches have often been selected to decrease the risk of posterior dislocation. Traditional anterolateral approaches have divided the anterior portion of the gluteus medius and minimus and potentially jeopardized the superior gluteal nerve. These disadvantages have been associated with abductor weakness, prolonged limp and decreased patient satisfaction. To overcome these problems, a mini-incision approach was developed using the intermuscular plane between the gluteus medius and the tensor fascia lata. This intermuscular interval through a small incision provides good exposure for total hip replacement and preserves muscle integrity so that rehabilitation can be rapid and the posterior capsule remains intact so that posterior dislocation is less of an issue. The surgical technique for this new innovative approach is described in this article.