Dislocation After Total Hip Arthroplasty Mazloumi MD

Patient Risk Factors Neuromuscular and cognitive disorders Patient noncompliance Previous hip surgery

Surgical Considerations Approach Soft-tissue tension Component positioning Impingement Head size Acetabular liner profile Surgeon experience

Treatment Closed reduction Revision options should target the underlying etiology. 1- Tensioning or Augmentation of soft tissues 2- Capsulorrhaphy 3- Trochanteric advancement 4- Correction of malpositioned of components 5- Improving the head – neck ratio

Surgical Approach 75% to 90% of dislocations are in the posterior direction Dislocation rate was 5.8% after a posterior approach versus 2.3% after an anterolateral approach (P < 0.01). Woo RY, Morrey BF: Dislocations after total hip arthroplasty. J Bone Joint Surg Am 1982;64:1295-1306

Surgical approches A recent meta-analysis involving 13,203 procedures dislocation rate : 3.23% Posterior approach 2.18% Anterolateral, approach 1.27% Transtrochanteric, approach 0.55% Direct lateral approach. Masonis JL, Bourne RB: Surgical approach, abductor function, and total hi arthroplasty dislocation. Clin Orthop 2002;405:46-53.

Surgical approach Larger heads (32 mm versus 22 and 28 mm) Definitive posterior soft-tissue repair These two influential elements (head size and soft-tissue tension) therefore may reduce or eliminate the disadvantage of the posterior approach with respect to instability. Goldstein WM, Gleason TF, Kopplin M, Branson JJ: Prevalence of dislocation after total hip arthroplasty through a posterolateral approach with partial capsulotomy and capsulorrhaphy. J Bone Joint Surg Am 2001;86:2-7.

Soft-Tissue Tension Meticulous reconstruction of the posterior capsule and short external rotators after a posterior approach was shown to reduce dislocation from 4.1% to 0.0% at 1-year followup in a study of 395 patients. Pellicci PM, Bostrom M, Poss R: Posterior approach to total hip replacement using enhanced posterior soft tissue repairClin Orthop 1998;355:224-228.

Soft-Tissue Tension Soft-tissue tension also can be greatly affected by femoral offset Trochanteric nonunion increased the dislocation rate sixfold (17.6% versus 2.8%; P < 0.001). large mismatch between femoral head size and acetabular component size (>64 mm cap <26 mm head )

Component Positioning Cup abduction of 40° ± 10° is considered to be the “safe zone” of lower dislocation risk. Cup anteversion should be 20° ± 5° Outside this safe range, dislocation in one study increased fourfold (6.1% versus 1.5%; P < 0.05) Lewinnek GE, Lewis JL, Tarr R, Compere CL, Zimmerman JR: Dislocations after total hip-replacement arthroplasties. J Bone Joint Surg Am 1978;60:217- 220.

Component Positioning The pelvis of a patient in the decubitus position may be significantly adducted and anteverted relative to the table. Adequate acetabular anteversion may be more critical with a posterior approach because it reduces forces on weakened posterior soft tissues

Impingment Impingement occurs when the prosthetic femoral neck impinges against the liner or other sessile object, such as cement, osteophyte, or heterotopic ossification . head-to-neck ratio is important. Components with higher ratios impinge less readily

Impingment

Head size The improved head-to-neck ratio reduces component impingement and increases ROM. Larger heads are seated deeper within the acetabular liner, requiring greater translation before dislocation “jump distance”

Head size Polyethylene wear increases with larger heads and thinner liners, and wear leads to periprosthetic osteolysis and the potential for loosening.

Liner Profile A, Standard. B, Elevated rim. C, Oblique. D, Lateralized

Surgeon Experience In their study of more than 4,000 primary found that surgeons who had performed fewer than 30 procedures had a markedly higher dislocation rate (approximately twofold) Hedlundh U, Ahnfelt L, Hybbinette CH, Weckström J, Fredin H: Surgical experience related to dislocations after total hip arthroplasty. J Bone Joint Surg Br 1996;78:206-2

Revision

Dislocations within weeks or months Problems with soft-tissue tension : 1- muscle weakness. 2- inadequate capsular healing and scarring. 3- component malposition. 4- infection. 5- patient noncompliance. Late dislocations (beyond 1 year) may suggest : 1- stretching of the soft tissues 2- polyethylene wear.

Salvage procedures Constrained cup implantations Dual-mobility hip components Bipolar Femoral Endoprosthesis Soft-tissue grafts Girdlestone resection

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