A Comparison of Revision Rates and Dislocation After Primary Total Hip Arthroplasty with 28, 32, and 36-mm Femoral Heads and Different Cup Sizes: An Analysis of 188,591 Primary Total Hip Arthroplasties

Artificial Intelligence-Based Surgery Support Model Using Intraoperative Radiographs for Assessing the Acetabular Component Angle

BACKGROUND

This study aimed to develop an artificial intelligence (AI)-based surgical support model for assessing the acetabular component angle using intraoperative radiographs during total hip arthroplasty and verify its accuracy.

METHODS

A total of 268 hips were analyzed. At first, 268 preoperative and intraoperative antero-posterior pelvic radiographs were amplified to 536. These radiographs were used to create a learning model to estimate the acetabular component angle from the radiographs intraoperatively. The ground truth was the anteversion and inclination angles obtained from the computed tomography (CT)-based navigation system intraoperatively. Bone landmarks on the preoperative and intraoperative radiographs were manually annotated. The distances and angles between each landmark were used as predictor variables. The estimation accuracy was assessed for internal and external test datasets. Mean absolute error (MAE) and R2 values were used as accuracy measures.

RESULTS

The MAE and R2 for the internal test set showed 2.19 and 0.850 for anteversion, and 1.18 and 0.805 for inclination, respectively. The MAE and R2 for the external test set showed 2.78 and 0.789 for anteversion, and 1.56 and 0.744 for inclination, respectively.

CONCLUSION

We developed an AI-based surgical support model for accurately assessing the acetabular component angle using intraoperative radiographs. Excellent estimation accuracy was confirmed for the external test set. In the future, the model may help to reduce the risk of adverse postoperative events.

Callus formation after total hip arthroplasty using a short tapered-wedge stem

OBJECTIVE

The incidence of periprosthetic fractures after total hip arthroplasty using a short tapered-wedge stem is high. Callus formation preceding this fracture, which indicates postoperative stress fracture around the stem, has been reported. However, previous studies on postoperative callus are limited. Hence, the current study aimed to evaluate the prevalence and risk factors of postoperative callus after total hip arthroplasty with a short tapered-wedge stem.

MATERIALS AND METHODS

This retrospective study included 127 patients who underwent total hip arthroplasty using a cementless short tapered-wedge stem. The depth of stem insertion was measured as the distance from the lateral corner of the stem to the most medial point of the lesser trochanter along the body axis. Postoperative callus was defined as a bridging callus on the lateral femoral cortex at the distal end of the porous coating of the stem. Plain radiography was performed before surgery and immediately and at 1, 3, and 6 months after surgery to assess postoperative callus. Univariate and multivariate logistic regression analyses were performed to identify the risk factors for PC.

RESULTS

In total, 60 (47.2%) of 127 patients presented with postoperative callus. Multivariate logistic regression analysis with postoperative callus as the dependent variable revealed that the stem depth at 1 month after total hip arthroplasty (odds ratio, 1.14; 95% confidence interval, 1.04-1.24, p = 0.002) was a significant and independent risk factor of postoperative callus.

CONCLUSION

Deep insertion of a short tapered-wedge stem is a risk factor for postoperative callus.

The impact of femoral head size on the wear evolution at contacting surfaces of total hip prostheses: A finite element analysis

Total Hip Arthroplasty has been a revolutionary technique in restoring mobility to patients with damaged hip joints. The introduction of modular components of the hip prosthesis allowed for bespoke solutions based on the requirements of the patient. The femoral stem is designed with a conical trunnion to allow for assembly of different femoral head sizes based on surgical requirements. The femoral head diameters for a metal-on-polyethylene hip prosthesis have typically ranged between 22 mm and 36 mm and are typically manufactured using Cobalt-Chromium alloy. A smaller femoral head diameter is associated with lower wear of the polyethylene, however, there is a higher risk of dislocation. In this study, a finite element model of a standard commercial hip arthroplasty prosthesis was modelled with femoral head diameters ranging from 22 mm to 36 mm to investigate the wear evolution and material loss at both contacting surfaces (acetabular cup and femoral stem trunnion). The finite element model, coupled with a validated in-house wear algorithm modelled a human walking for 10 million steps. The results have shown that as the femoral head size increased, the amount of wear on all contacting surfaces increased. As the femoral head diameter increased from 22 mm to 36 mm, the highly cross-linked polyethylene (XLPE) volumetric wear increased by 61% from 98.6 mm3 to 159.5 mm3 while the femoral head taper surface volumetric wear increased by 21% from 4.18 mm3 to 4.95 mm3. This study has provided an insight into the amount of increased wear as the femoral head size increased which can highlight the life span of these prostheses in the human body.

Lower Risk of Revision With 32- and 36-Millimeter Femoral Heads Compared With 28-mm Heads in Primary Total Hip Arthroplasty: A Comparative Single-Center Study (10,104 Hips)

BACKGROUND

We aimed to compare the clinical outcomes of different head sizes (28-, 32-, and 36- millimeter) in primary total hip arthroplasty (THA) at mean 6 years follow-up (range, 1 to 17.5 years).

METHODS

This was a retrospective consecutive study of primary THA at our institution (2003 to 2019). Demographic and surgical data were collected. The primary outcome measures were all-cause revision, revision for dislocation, and all-cause revision excluding dislocation. Continuous descriptive statistics used means, median values, ranges, and 95% confidence intervals, where appropriate. Kaplan-Meier survival curves were used to estimate time to revision. Cox proportional hazard regression analyses were used to compare revision rates between the femoral head size groups. Adjustments were made for age at surgery, sex, primary diagnosis, American Society of Anesthesiologists score, articulation type, and fixation methods. There were 10,104 primary THAs included; median age was 69 years (range, 13 to 101) with 61.5% women. A posterior approach was performed in 71.6%. There were 3,295 hips with 28-mm heads (32.6%), 4,858 (48.1%) with 32-mm heads, and 1,951 (19.3%) with 36-mm heads.

RESULTS

Overall rate of revision was 1.7% with the lowest rate recorded for the 36-mm group (2.7 versus 1.3 versus 1.1%). Cox regression analyses showed a decreased risk of all-cause revision for 32 and 36-mm head sizes as compared to 28-mm; this was statistically significant for the 32-mm group (P = .01). Risk of revision for dislocation was significantly reduced in both 32-mm (P = .03) and 36-mm (P = .03) head sizes. Analysis of all cause revision excluding dislocation showed no significant differences between head sizes.

CONCLUSIONS

We found a significantly reduced risk of revision for all causes, but particularly revision for dislocation with larger head sizes. Concerns regarding increased risk of early revision for aseptic loosening, polyethylene wear, or taper corrosion with larger heads appear to be unfounded in this cohort of 10,104 patients with up to 17 years follow-up.

Excellent 20-Year Results of Total Hip Arthroplasty With Highly Cross-Linked Polyethylene on Cobalt-Chromium Femoral Heads in Patients ≤50 Years

BACKGROUND

Highly cross-linked polyethylene (HXLPE) acetabular bearing surfaces have appeared to offer excellent wear resistance, low incidence of wear-related osteolysis, and high implant survivorship at 10-year to 15-year follow-up. However, concerns over potential performance deterioration at longer-term follow-up remain - particularly in younger patients - and outcome data into the third decade have not been available.

METHODS

We retrospectively assessed 62 patients (68 hips) who underwent primary total hip arthroplasty (THA) at age ≤50 years with a single manufacturer's cementless components, remelted HXLPE liner, and small diameter (26 and 28 millimeter) cobalt-chromium (CoCr) femoral heads at minimum 18-year follow-up. We assessed clinical outcomes (modified Harris Hip score, University of California Los Angeles Activity Score, polyethylene wear rates, radiographic findings (osteolysis, component loosening), and implant survivorship.

RESULTS

At 20.6-year mean follow-up (range, 18 to 23 years) modified Harris Hip scores for surviving hips remained an average of 41 points above preoperative baseline (49 versus 90, P < .001) and UCLA scores 2.8 points above baseline (3.7 versus 6.4, P < .001). Wear analysis revealed a population linear wear rate of 0.0142 mm/y (standard deviation (SD), 0.0471) and volumetric wear rate of 10.14 mm3/y (SD, 23.41). Acetabular lysis was noted in 2 asymptomatic hips at 16.6 and 18.4 years. No components were radiographically loose. Survivorship free from wear-related revision was 100% at 20 years (97% free from any revision).

CONCLUSION

The HXLPE-CoCr bearing couple with small femoral heads continues to be extremely effective 20 years after primary THA in the younger patient population.

The True Dislocation Incidence following Elective Total Hip Replacement in Sweden: How Does It Relate to the Revision Rate?

(1) Background: The true dislocation incidence following THA is difficult to ascertain in population-based cohorts. In this study, we explored the cumulative dislocation incidence (CDI), the relationship between the incidence of dislocation and revision surgery, patient- and surgery-related factors in patients dislocating once or multiple times, and differences between patients being revised for dislocation or not. (2) Methods: We designed an observational longitudinal cohort study linking registers. All patients with a full dataset who underwent an elective unilateral THA between 1999 and 2014 were included. The CDI and the time from the index THA to the first dislocation or to revision were estimated using the Kaplan-Meier (KM) method, giving cumulative dislocation and revision incidences at different time points. (3) Results: 136,810 patients undergoing elective unilateral THA were available for the analysis. The 30-day CDI was estimated at 0.9% (0.9-1.0). The revision rate for dislocation throughout the study period remained much lower. A total of 51.2% (CI 49.6-52.8) suffered a further dislocation within 1 year. Only 10.9% of the patients with a dislocation within the first year postoperatively underwent a revision for dislocation. (4) Discussion: The CDI after elective THA was expectedly considerably higher than the revision incidence. Further studies investigating differences between single and multiple dislocators and the criteria by which patients are offered revision surgery following dislocation are urgently needed.

Mean 16-Year Results of Total Hip Arthroplasty with Alumina Ceramic Femoral Heads on Highly Cross-Linked Polyethylene in Patients 50 Years or Less

BACKGROUND

Highly cross-linked polyethylene (HXLPE) is a widely used bearing surface in total hip arthroplasty (THA); long-term results in young patients are limited. We previously demonstrated excellent results in HXPLE on cobalt-chrome femoral heads at 15-year mean follow-up. The purpose of the present study was to investigate polyethylene wear rates, implant survivorships, wear-related revisions, and patient-reported outcomes (PROs) in a young patient cohort who had alumina ceramic on HXPLE coupling at an average 16-year follow-up.

METHODS

This was a retrospective study of 128 hips who underwent THA with HXLPE on alumina ceramic bearings between March 1, 2004, and April 15, 2007. Patient mean age was 38 years (range, 13 to 50). All THAs utilized HXPLE liners with alumina ceramic heads. The University of California, Los Angeles (UCLA) Activity Score and modified Harris Hip Scores (mHHS) were collected pre-operatively and at each follow-up. Martell Hip Analysis Suite was used for wear calculations.

RESULTS

At average 16 years (range, 13 to 18), aseptic revision survivorship was 93.3% and osteolysis/wear survivorship was 99.2%. The mean linear wear rate was 0.0191 millimeters (mm)/year and mean volumetric wear rate was 19.43 mm³/year, both of which were clinically undetectable. We observed excellent patient reported outcomes with a significant increase in mean mHHS (43.6 to 87.4, P <0.0001) and UCLA Activity Scores (4.0 to 6.0, P <0.0001). There were no statistically significant differences in PROs or wear rates between ceramic and cobalt-chrome groups.

CONCLUSION

At mean 16-year follow-up, young patients who had HXLPE on ceramic coupling had excellent wear properties, PROs, and acceptable survivorships.

Highly crosslinked polyethylene liner thickness does not influence survival in primary total hip arthroplasty after mean follow-up of 13 years: a study of 2,565 hips with a single design liner

BACKGROUND

Concerns remain that thinner highly crosslinked polyethylene (HXLPE) liners in modern total hip arthroplasty (THA) may lead to premature liner-related failures or revision. The aim of this study was to evaluate the effect of liner-thickness on survival and revision rates of HXLPE in primary THA after more than 10 years.

METHODS

We retrospectively identified 2,565 primary THA using HXLPE with a mean follow-up of 13 years (range, 11 to 19). Patients were grouped for each millimeter (mm) of polyethylene thickness. Liner thickness varied from 4.9 to 12.7 mm, with one third measuring less than 6 mm. Primary outcomes were reoperation, all-cause revision, and liner-related revision.

RESULTS

The reoperation rate was 7.3%, the all-cause revision rate was 5.6%, and the liner-related revision rate was 0.04%. There was no significant difference in all-cause revision when stratified by liner thickness (P=0.286) and liner thickness was not associated with liner-related revision (n=1). There was a statistically, but not clinically significant difference in mean liner thickness for the cohort that underwent reoperation (7.09 vs 6.89 mm, P=0.01) and all-cause revision (7.16 vs 6.89 mm, P=0.031).

CONCLUSION

In our cohort, liner thickness was not associated with all-cause revision-free survival and there was no clinically significant difference in liner thickness between those patients who did require a reoperation or all-cause revision, and those who did not. There was only 1 liner related failure in the entire cohort. Our results indicate that using thinner HXPE liners to maximize femoral head size in THA is a safe practice that does not lead to increased revision rates or liner failure at a mean 13 years follow-up.