Thumb base arthritis, also known as carpometacarpal osteoarthritis, affects up to one in three women over fifty and is driven by failure of the anterior oblique (beak) ligament. The grind test reproduces pain by axial compression with rotation, while Eaton–Littler staging on a single radiograph guides treatment. This video explores the anatomy, diagnosis, staging and the evidence behind ligament reconstruction and tendon interposition (LRTI). ⏱ Chapters 0:00 Intro 0:56 A Saddle Built For Reach, Not Stability 1:54 The Restraints — Volar And Dorsal, Model… 2:49 Recognising It 3:33 Robert'S View — The True AP Of The Thumb… 4:03 Four Stages, One Radiograph 4:49 Staging Is The Treatment Map 5:49 What Actually Helps 7:01 Inside The Operation 7:41 The Operative Checklist 8:21 The Failure Mode — Subsidence And Lost… 8:53 Recap & sources The video details the saddle‑joint anatomy of the thumb carpometacarpal articulation, explains how attenuation of the beak ligament initiates dorsoradial subluxation and cartilage wear, demonstrates the grind test and its interpretation, walks through Eaton–Littler radiographic staging, compares conservative and surgical options by stage, and critically appraises the current evidence for ligament reconstruction and tendon interposition versus simple trapeziectomy. Understanding these points is essential for accurate diagnosis, appropriate staging, and informed treatment decisions for this common source of thumb pain. 🦴 IN THIS VIDEO YOU'LL LEARN • Identify the saddle joint anatomy of the thumb CMC articulation • Recognise how attenuation of the anterior oblique (beak) ligament initiates dorsoradial subluxation • Perform and interpret the grind test for thumb base arthritis • Apply Eaton–Littler staging using a single radiograph • Differentiate thumb CMC arthritis from De Quervain’s tenosynovitis and scaphotrapezial arthritis • Summarise conservative and surgical treatment algorithms by stage • Critically appraise the evidence for ligament reconstruction and tendon interposition (LRTI) versus simple trapeziectomy • Explain postoperative expectations and satisfaction rates after trapeziectomy with LRTI 📌 KEY TAKEAWAYS ✔️ The anterior oblique (beak) ligament is the primary stabiliser; its failure starts thumb CMC arthritis. ✔️ A positive grind test is pathognomonic for symptomatic thumb base arthritis. ✔️ Eaton–Littler stage III–IV disease usually warrants surgical intervention, most commonly trapeziectomy with LRTI. ✔️ Current evidence shows no clear superiority of adding LRTI to trapeziectomy, yet patient satisfaction remains over 90%. 👩⚕️ WHO THIS IS FOR This video is designed for orthopaedic trainees, medical students, hand therapists and clinicians managing thumb pain, as well as informed patients seeking to understand their condition. 📚 RELATED TOPICS: De Quervain's tenosynovitis · Scaphotrapezial-trapezoid (STT) arthritis · Thumb metacarpophalangeal joint hyperextension · Trapeziectomy techniques · Ligament reconstruction and tendon interposition (LRTI) outcomes · Basal thumb joint splinting 🔗 More free orthopaedic teaching at Orthovellum.com — subscribe for weekly videos. 🎨 CREDITS • Original Orthovellum production. ⚠️ DISCLAIMER: Educational only — not individual medical advice. Always consult a qualified clinician for diagnosis and treatment. #orthopaedics #handsurgery #thumbarthritis #cmcarthritis #grindtest #eatonlittler #lrtit #trapeziectomy #beakligament #thumbpain #handanatomy #osteoarthritis #jointsurgery #patienteducation #musculoskeletal