arthroplasty
Extensor Mechanism Disruption After TKA
advanced
6 min
20 marks
5 questions
Clinical Scenario
A 68-year-old man felt a pop in his knee when rising from a chair 2 weeks ago. He has a 5-year-old TKA for osteoarthritis. Now unable to extend his knee against gravity. On examination, there is significant swelling, bruising over the anterior knee, and a palpable gap inferior to the patella. He has diabetes and takes prednisone for COPD.
Lateral radiograph showing TKA with high-riding patella (patella alta). Visible gap between inferior patella and tibial tubercle region. Patellar component appears intact. TKA components well-positioned.
Image source: Open Access medical literature (NIH/PubMed Central) • CC-BY License
Questions
Question 1 (3 marks)
What is the diagnosis, classification, and risk factors for this injury?
Question 2 (4 marks)
Describe the challenges of managing extensor mechanism disruption after TKA.
Question 3 (5 marks)
What surgical options are available for patellar tendon rupture after TKA?
Question 4 (4 marks)
Describe extensor mechanism allograft reconstruction technique.
Question 5 (4 marks)
What postoperative protocol and rehabilitation would you recommend?
Exam Day Cheat Sheet
Must Mention
- •Patella alta on lateral XR = patellar tendon rupture
- •Direct repair fails 40-50% - ALWAYS augment
- •Allograft (extensor mechanism or Achilles) for chronic/failed repairs
- •Risk factors: diabetes, steroids, CRF, RA, multiple surgeries
- •Protect repair: locked extension brace 6 weeks
- •Expect residual extension lag (10-20° acceptable)
Common Pitfalls
- •Direct repair without augmentation
- •Early active knee flexion
- •Not recognizing chronic rupture
- •Over-tensioning reconstruction
- •Unrealistic outcome expectations