Instability Introduction incidence common cause of early failure following total knee arthroplasty accounts for 10-20% of revisions types extension (varus-valgus) instability flexion (anteroposterior) instability mid-flexion instability genu recurvatum global, multiply-operated instability Presentation History previous operations indication for initial replacement original implant information comorbidities including connective tissue disease inflammatory diseases diabetes, Charcot arthropathy history of trauma Symptoms pain, instability or both timeline as to start of symptoms, what worsens/improves Physical Examination overall gait, observe for valgus/varus thrust ligamentous examination throughout range of motion, attempt to reproduce symptoms flexion instability test positive posterior sag with the knee flexed to 90 degrees overall strength extensor mechanism competency patellar tracking Imaging Radiographs recommended views weightbearing AP used to assess joint line symmetry full-length AP used to assess overall mechanical alignment lateral used to assess tibial slope, tibial subluxation, recurvatum findings extension instability excessive distal femoral resection oversized femoral component flexion instability overresection of posterior femoral condyles undersized femoral component increased tibial slope mid-flexion instability anterior or proximal placement of femoral component genu recurvatum Computed tomography can offer information regarding component rotation Studies Serum labs CBC, ESR, CRP, must rule out infection as potential cause Knee aspiration to rule out infection via cell count and culture Extension (varus-valgus) Instability Definition varus/valgus instability types symmetrical caused by excessive distal femoral resection, causing flexion/extension gap mismatch asymmetrical more common ligamentous asymmetry caused by failure to correct deformity in the coronal plane Treatment symmetrical instability distal femoral augments to tighten extension gap upsizing poly will fail as it affects both flexion and extension gaps asymmetrical instability balance ligaments accordingly controlled release of soft tissue on contracted side if ligamentously insufficient, varus/valgus constrained device needed if caused by, intraoperative MCL transection/deficiency suture repair or suture anchor reattachment, use of either CR or PS implant, hinged knee brace for 6 weeks postoperatively use of unlinked constrained prosthesis Flexion (anteroposterior) instability Definition occurs when the flexion gap exceeds the extension gap knee dislocation posterior stabilized knees can "jump the post" resulting in dislocation Treatment over resection of posterior femoral condyles treat with posterior augments undersizing femoral component upsize femoral component excessive tibial slope decrease slope and consider posterior-stabilized prosthesis excessive posterior femoral condyle cuts augment posterior condyles of distal femur posterior cruciate ligament insufficiency following a cruciate-retaining arthroplasty convert to posterior-stabilized prosthesis Mid-flexion instability Causes controversial topic, poorly understood associated with modification of the joint line involves malrotation when the knee is flexed between 45 and 90 degrees potential contributing factors femoral component design in sagittal plane attenuation of anterior MCL overall geometry of the tibiofemoral joint Treatment typically, full revision is required goals restoration of joint line equalize flexion and extension gaps Genu recurvatum Definition fixed valgus deformity and iliotibial band contracture Causes associated with poliomyelitis, rheumatoid arthritis, or Charcot arthropathy poliomyelitis patient walks with knee locked in hyperextension, ankle in equinus due to quadriceps weakness Treatment typically long-stemmed posterior stabilized, or varus/valgus constrained implant rotating-hinge reserved for salvage as residual hyperextension may occur, leading to early failure Global, multiply-operated instability Definition laxity of both flexion and extension gaps, as well as varus/valgus instability can be associated with severe bone loss Presentation multidirectional ligamentous instability with recurvatum gait Treatment varus/valgus constrained prosthesis at minimum typically, hinged prosthesis with or without augments, sleeves, cones severe bone loss situations may require endoprosthetic replacements
Technique Guide Technique guide are not considered high yield topics for orthopaedic standardized exams including the ABOS, EBOT and RC. TKA Revision Orthobullets Team Recon - High Tibial Osteotomy Technique Guide Technique guide are not considered high yield topics for orthopaedic standardized exams including the ABOS, EBOT and RC. TKA - Parapatellar Approach Derek Bernstein Stephen Incavo Recon - High Tibial Osteotomy Technique Guide Technique guide are not considered high yield topics for orthopaedic standardized exams including the ABOS, EBOT and RC. TKA - Varus Knee with Anterior Referencing and Gap Balancing Technique Derek Bernstein Stephen Incavo Recon - TKA Axial Alignment
QUESTIONS 1 of 8 1 2 3 4 5 6 7 8 Previous Next Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (OBQ09.230) A 66-year-old female presents with knee instability going down stairs 18 months after a posterior cruciate retaining total knee arthroplasty. She reports having recurrent effusions. Radiographs are shown in Figure A. What is the most likely cause for her instability? Review Topic | Tested Concept QID: 3043 FIGURES: A Type & Select Correct Answer 1 Intraoperative rupture of the patellar tendon 2% (49/2671) 2 Alteration of the joint line 2% (53/2671) 3 Posterior cruciate insuffiency 94% (2513/2671) 4 Anterior cruciate insufficiency 1% (20/2671) 5 Catastrophic component loosening 1% (21/2671) L 1 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review tested concept Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK This is an AAOS Self Assessment Exam (SAE) question. Orthobullets was not involved in the editorial process and does not have the ability to alter the question. If you prefer to hide SAE questions, simply turn them off in your Learning Goals. (SAE07HK.7) Figure 3 shows the AP radiograph of a patient with diabetes mellitus who has knee pain. A semiconstrained knee prosthesis was used in this patient to prevent which of the following complications? Review Topic | Tested Concept QID: 5967 FIGURES: A Type & Select Correct Answer 1 Infection 0% (0/465) 2 Instability 97% (453/465) 3 Stiffness 0% (1/465) 4 Bone loss 1% (4/465) 5 Malalignment 1% (6/465) L 1 Question Complexity E Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 2 Review tested concept Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK
All Videos (8) Podcasts (1) Login to View Community Videos Login to View Community Videos 2017 Orthopaedic Summit Evolving Techniques TT-TTG: Too Many Initials - What Does It Mean? How Do I Measure It? Is It CT? Is It MRI? Help Please! - Beth E. Shubin-Stein, MD Recon - TKA Instability 4/30/2018 218 views (1) Login to View Community Videos Login to View Community Videos 2017 Orthopaedic Summit Evolving Techniques Patellofemoral Instability: Perfecting the Distal Patellofemoral Realignment with Outcomes - Jason L. Koh, MD, MBA Recon - TKA Instability 4/30/2018 101 views (1) Login to View Community Videos Login to View Community Videos 2017 Orthopaedic Summit Evolving Techniques Trochlear Dysplasia: What Is It All About, How Do I Treat It - David R. Diduch, MD, MS Recon - TKA Instability 4/30/2018 142 views (0) Recon⎪TKA Instability Orthobullets Team Recon - TKA Instability Listen Now 16:21 min 6/4/2020 42 plays (0) See More See Less
Windswept Knees in 69F (C101409) Shaun Patel Recon - TKA Instability B 3/26/2020 31 0 6 Severe Valgus Knee in 58F (C101405) Shaun Patel Recon - TKA Instability E 3/22/2020 97 10 2