Neurosurgery notes/Procedures/TL spine procedures/Lumbar disc arthroplasty

Lumbar disc arthroplasty

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TL spine procedures

Types of lumbar artificial disc (LAD)

  • Articulating LADs
      • Using a ball and socket principle
      • Classification:
        • Nonconstrained LAD: No specific limitation in mobility.
          • More constrained LADs: Greater risk of adverse sequelae from imperfect primary placement.
        • Semiconstrained LAD: Allows partial or no translation.
          • Less constrained LADs: Greater mechanical stresses on posterior joints.
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  • Nonarticulating LADs
    • Developed due to the failure of articulating LADs to replicate native disc elasticity.
      • Aim to emulate shock absorptive and flexural stiffness of the natural intervertebral disc more closely.
    • Challenges in Development:
      • Identifying biocompatible materials (increased periprosthetic tissue reaction potential due to particle generation).
      • Materials resistant to wear and tear.
      • Materials providing sufficient adhesion to vertebral bodies.

Complications (Beatty 2018)

Nonspinal Complications of LTDR
  • Intraoperative:
    • Complicatios of anterior lumbar surgical approach
      • Injury to ureter, nerves, or large vessels.
  • Postoperative:
    • Infection
    • Wound problems
    • Hematoma
    • Common to all LTDR procedures using an anterior lumbar surgical approach, regardless of the LAD used.
      • Retrograde ejaculation
      • Formation of retroperitoneal lymphocele
  • Less-invasive lateral or laparoscopic approaches may help reduce risk but still being investigated
Spinal Complications of LTDR
  • Classed as attributable to LAD malposition or occurring despite optimal LAD anchorage.
Spinal LTDR Complications Attributable to LAD Malposition
  • Malposition can be due to:
    • Suboptimal placement/anchoring of the LAD at the Time of Surgery
      • LTDR is technically challenging.
      • First-generation LADs (e.g., SB Charite) had a steep learning curve; suboptimal placement seen in 60% of cases.
      • Ideal LAD placement associated with better clinical/functional outcomes.
    • Postoperative migration or subsidence.
Spinal LTDR Complications Unrelated to LAD Malposition
Periprosthetic Wear Debris
  • Biological responses to wear debris can cause spinal complications.
  • ProDisc-L: Metal-on-polyethylene design (cobalt-chromium endplates, UHMWPE core).
  • Wear of UHMWPE core observed in several metal-on-polyethylene LADs, with adverse clinical implications.
  • Can lead to osteolysis, subsidence, migration, fusion.
Facet degeneration (Arthrosis)
  • LTDR compromises anterior longitudinal ligament and annulus fibrosus, raising concerns about rotational instability.
  • Most important determinant of postoperative index/adjacent-level vertebral rotation is preoperative ROM.
  • Spinal instability concerns have profound implications for facet joints (true synovial joints, part of 3-joint complex).
    • Facet joints aid in inhibiting rotation and excess motion for vertebral alignment.
    • Disc is primary load-bearing structure (up to 33% total load); decreased support by disc in narrowed/incompetent discs shifts load to facets.
    • Up to 70% of axial load borne by facets in severe LDDD, predisposing to facet arthrosis.
  • Biomechanical studies:
    • Ball-and-socket LADs (e.g., ProDisc-L) increase facet loading at surgical level (especially L4-L5, L5-S1), more evident during lateral bending/axial rotation.
    • Posterior prosthesis placement provides more physiologic load transfer.
    • May increase ROM under axial load but maintain helical axis of motion with similar facet contact forces to intact spine.
    • Degree of LAD constraint affects kinematics/load transfer: semiconstrained LADs partially unload facets compared to unconstrained.
  • Occurs in around 30-40% of patients
  • Lumbar disc degenerative disease is a risk factor for facet arthrosis, as are surgical procedures to alleviate its symptoms (lumbar interbody fusion, lumbar discectomy, and LTDR).
Heterotopic Ossification (HO)
  • Presence of bone in soft tissue where it doesn't normally exist.
  • Categorized:
    • Class 0 (no HO)
    • Class IV (bony ankylosis).
  • Study (65 patients/82 LADs, ProDisc or SB Charite): HO in 30.5% segments (9.8% Class I, 14.6% Class II, 6.1% Class III).
  • No difference in ROM, VAS, Oswestry Disability Index between Class I/II and no HO.
  • Class III HO: Comparable VAS/Oswestry with no HO, but significantly less segmental ROM.
  • Can lead to
    • Reduced ROM
    • Radicular pain
    • Osteolysis.
Osteolysis
  • Bone destruction at bone-implant interface after orthopedic arthroplasty.
  • Due to implant micromotion and body's response to wear debris (inflammatory process, increased bone resorption).
  • Low prevalence after LTDR (compared to total hip replacement) attributed to small ROM of LADs.
Vertebral Body-Splitting Fractures
  • Rare after single-level LTDR
  • More common after multilevel LTDR associated with sclerotic fracture margins.
  • Risk can be reduced by modifying surgical technique.