Relative Contribution of Acetabular and Femoral Reconstruction to Prosthetic Joint Instability Risk after Primary Total Hip Arthroplasty

Abstract

Prosthetic joint instability is a challenging concern for a minority of total hip arthroplasty (THA) patients. Placement of the acetabular component within the traditional safe zone does not eliminate dislocation, and the relative contribution of femoral length and offset to instability risk has not been well defined. The authors compared 53 dislocated primary THAs treated against an age- and gender-matched cohort of 134 stable primary THAs. Anteroposterior and cross-table lateral radiographs were used to determine whether reconstructions met targets for acetabular inclination (30–50 degrees), acetabular anteversion (5–30 degrees), femoral length (0–9.9 mm) and femoral offset (0–9.9 mm). Statistical analysis was performed to assess univariate and multivariate relationships with an instability event; statistical significance was set using a two-sided p-value < 0.05. Forty-seven (88.7%) of the dislocating hips had nonoptimal acetabular or femoral reconstructions. While a similar proportion of patients in the study and control groups had acetabular reconstruction within the safe zone (51.5 vs. 47.2%, p = 0.63) patients with unstable hips were more likely to have acetabular component inclination outside of the target zone (30.2 vs. 7.5%, p < 0.01), acetabular anteversion < 15 degrees (30.2 vs. 3.7%, p < 0.0001), reduced femoral length (35.9 vs. 3.7%, p < 0.0001), and reduced femoral offset (41.5 vs. 7.46%, p < 0.0001). Stepwise multivariate logistic regression was performed and identified femoral head size less than 32 mm (OR 2.9, 95% CI 1.4–6.2) and higher inclination angle (OR 1.1, 95% CI 1.04–1.2) as significant independent risk factors for hip instability. The authors' study findings suggest that insufficient acetabular anteversion, femoral length, and femoral offset reconstruction contribute significantly to instability risk following THA. Using a larger femoral head is protective, but should be balanced against long-term volumetric wear risk.

Intraoperative Imaging Improves Posterolateral THA Accuracy with Increased Time Cost

“…Limb length discrepancies and poor femoral offset restoration have been associated with hip pain, low back pain, weakness, gait abnormality, THA instability, and polyethylene wear. 26 27 28 29 30 31…”

“…Limb length discrepancies and poor femoral offset restoration have been associated with hip pain, low back pain, weakness, gait abnormality, THA instability, and polyethylene wear. [26][27][28][29][30][31] The use of intraoperative imaging increased mean operative time by 11.4 minutes with a $1,200 increase in operating room charges per procedure. Acetabular component repositioning occurred in 21.5% of cases assessed with digital radiography and was associated with a 10-minute increase in operative time and $738 increase in operating room Imaging Improves THA Accuracy and Cost Ralston et al…”

Preoperative Leg Length Discrepancy >2 cm in the Supine Decubitus Position May Induce Compensatory Pelvic Obliquity in Patients during Total Hip Arthroplasty

“… 4 , 5 , 6 , 7 To obtain a balance between high dislocation and high wear rates, it is widely acceptable to implant the acetabular component at an ideal inclination angle of 30°–50°. 8 , 9 …”

“…An increased risk of dislocation has been demonstrated when the cup is placed at a high inclination angle 3,4 ; however, a low inclination of the acetabular component is associated with several complications, including postoperative impingement, a high wear rate, and loosening 4–7 . To obtain a balance between high dislocation and high wear rates, it is widely acceptable to implant the acetabular component at an ideal inclination angle of 30°–50° 8,9 …”

“…[4][5][6][7] To obtain a balance between high dislocation and high wear rates, it is widely acceptable to implant the acetabular component at an ideal inclination angle of 30 -50 . 8,9 Although computer-assisted and imageless navigation procedures have been reported to achieve accurate positioning of the acetabular component, 10,11 many surgeons prefer to use a free-hand technique because of the shorter operative time and lower cost. A fixed patient position and apparent anatomic landmarks of the pelvis are essential for the accuracy of acetabular component implantation during free-hand THA.…”