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What is in Shoulder Arthroplasty ?

What is in Shoulder Arthroplasty ?. Nadhaporn Saengpetch, MD. Cookbook for Total Shoulder Arthroplasty . Objectives. Have a basic understanding of the relevant anatomy for shoulder arthroplasty To know the biomechanic and clinical application of conventional arthroplasty .

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What is in Shoulder Arthroplasty ?

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  1. What is in Shoulder Arthroplasty ? Nadhaporn Saengpetch, MD.

  2. Cookbook forTotal Shoulder Arthroplasty

  3. Objectives • Have a basic understanding of the relevant anatomy for shoulder arthroplasty • To know the biomechanic and clinical application of conventional arthroplasty

  4. Goal of Arthroplasty • To restore comfort motion and function that lost from OA • Host acceptance of prosthesis and implant longevity

  5. Summary Design History • The Neer II implant(nonmodular) • Early 1990s : more secure fixation, longer stems, bigger bodies and modularity between heads and stems • The modular designs : mix & match various stems and head sizes

  6. Neer II Prosthesis

  7. Modern Modular Systems • Mismatch anatomic and prosthetic head • Prosthetic collars and taper lock of the modular head

  8. Anatomic-Prosthetic Mismatch

  9. Glenoid Issues • Original keeled implants* by Dr.Neer are still popular • All-polyethylene* • Metal-backed • pegged

  10. Contents • Anatomy-Biomechanic and implant considerations • Technical considerations Disease-specific considerations

  11. AnatomicConsiderations

  12. Humerus

  13. Retroversion • Variably individual, depends on methodology used • Ranged from 0º to 55º • Different axes are used Trans-epicondylar axis

  14. Head Shaft Angle (HSA) • Ranged from 30º-55º • ?articular surface • ?humeral canal shape (a proximal is conical)

  15. Offset(OS) • Characterized by the distance of center of rotation from the central axis of the canal • Medial 4-14 mm • Posterior -2-10 mm

  16. Radius of Curvature (RC) & Head Height(HH) • Coronal RC is greater than sagittal RC • Range 20-30 mm, M > F • HH depends on the thickness of the articular surface • Regardless of head size, HH:RC ratio is about ¾ • Arc of humeral surface is 150º

  17. Sagittal Plane RC HH

  18. Anatomic Dimensions of GHJ Iannotti JP Disorder of the Shoulder, Philadelphia : LW&W 1999, p.472

  19. Glenoid

  20. Retroversion • A pear shape • Slightly retroverted relative to the scapular plane • The measurement is vary • Width : Height is ¾ • The height is 4 cm

  21. Bi-concave Glenoid • Post stabilization procedure for ADI • Chronic GHJ arthritis

  22. Biomechanic Considerations

  23. Biomechanic Factors • The congruent glenoid surface and humeral head allows the compressive force across this ball-and-socket joint • 50% of the resistance to translation comes from a labrum

  24. mid-range : concavity compression • Extreme motion : capsular constraint anterior/inferior MGHL & IGHL superior SGHL & CHL posterior posterior capsule

  25. Rotator Cuff : Dynamic • Imparting a compressive force • Restraining HH translation • Creating a strap effect over the joint • Force couple with the deltoid

  26. Implant Considerations

  27. The Head&Stem

  28. Humeral Head Size • Modularity : the collar and taper mechanism must be considered • Identical replication • An anatomic head radius (RC) is between 20-30 mm • HH thickness 5 mm, ROM 20º-30º

  29. Relationships of Normal Humeroscapular Preparations Harryman DT JBJS Am 1995:77A:555-63

  30. Anatomic-sized HH Replacement Harryman DT JBJS Am 1995:77A:555-63

  31. Oversized HH Replacement Net lateral humeral shift = 3.5+2 = 5.5 mm Net lateral humeral shift = 5+2 = 7 mm Harryman DT JBJS Am 1995:77A:555-63

  32. Again!

  33. Humeral Head Size • Significant glenoid bone loss (RA*) - medialization of GHJ - slacken the soft tissues • Decrease HH thickness - point loading the glenoid - alteration of GH translation - tuberosity impingement • In vivo, smaller is better

  34. Humeral Head Osteotomy • Surgeons’ dependent • The inclination angle of the prosthesis • Intramedullary guide (fixed) • Bone graft/cement • Approximation of anatomic inclination ~ balance/stable GHJ

  35. Humeral Head Osteotomy • 30º-45º retroversion • Externally rotating the arm • Rotator cuff detachment*

  36. Head-Stem Relationship • Different length stems • Flute/smooth • Cylindrical/taper • Size increment • Metaphyseal region variation • An eccentric locking position of the morse taper (M-P OS)

  37. OS MechanismMedio-posterior OS

  38. Head-Stem Relationship

  39. Head-Stem Relationship • Too superior : tension on SSP, pinching the acromion • Too inferior : abutment of GT on acromion, glenoid rim internal impingement

  40. Head-Stem Relationship • Too anterior : abutment of uncovered humeral neck on SSC • Too posterior : abutment of uncovered humeral neck on posterior cuff tendons (ISP+TM) • 3-4 mm offset • Still unclear benefit between flexible and rigid systems*

  41. The Glenoid • PE durability thickness • >4 mm thick lateralize GHJ • Shape : something between a rectangle and an oval • ? Pear shape • metal backed (PE wear, dissociation) • Pegged and keeled*

  42. The Glenoid

  43. The Glenoid • OA GHJ : posterior glenoid wear and nonanatomic retroversion • Power reaming to a curvature matching the back of the glenoid component

  44. Glenohumeral Relationship • Conformity and constraint • Cartilage & labrum flexibility >> PE, cobalt flexibility • Natural prosthetic kinemetic may not be optimal durability • GHJ translation and conformity only applied under active joint loading*

  45. Conformity & Constraint

  46. Glenohumeral Translation

  47. Radial Mismatch • point loading, PE wear • *Better x-ray durability for radial mismatch > 6 mm (Walch G JBJS Am Dec,2002)

  48. Technical Consideration

  49. Humerus • Geometry : 3D proximal humerus • 1st& 2nd generation are problematic • 2 arbitrarily fixed angles 1) inclination 2) retroversion

  50. Humerus • Cut : using the anatomic neck as a landmark (!!distorted neck) • 3rd generation prosthesis : adjustable inclination & OS

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