Usefulness of a Simple Preoperative Planning Technique using Plain X-rays for Direct Anterior Approach for Total Hip Arthroplasty.

OBJECTIVE

To examine the accuracy, reliability, and reproducibility of a simple preoperative planning technique using plain X-rays.

METHODS

A retrospective analysis of 96 consecutive cases of primary direct anterior approach (DAA)-total hip arthroplasty (THA) from July 2015 to December 2018 was performed. The 96 patients included 24 males and 72 females, with an average age of 70 years. The standard AP pelvis radiographs with the patients' hips extended and internally rotated were obtained pre- and postoperatively. The preoperative planning was also completed on the standardized AP pelvic radiographs. The prearranged cup positioning was radiologically measured intraoperatively using fluoroscopy. The correct leg length was assessed intraoperatively, which was compared with the preoperative planning. The component positioning was measured by three independent researchers. Two of the researchers completed the measurements three times, and intra-observer and inter-observer reliability were calculated. All patients received at least 6 months follow-up (6 months-4 years).

RESULTS

In all cases, the median leg length discrepancy (LLD) was 4.4 mm (range 1.6-15.9 mm), and 84 patients had an LLD smaller than 10 mm, of which 58 patients had an LLD of less than 5 mm. None of the patients had a critical LLD of 2 cm or larger. The multivariable logistic regression for LLD (safe range: yes/no) with the co-variables including gender, ASA classification, type of cup, the surgeon's experience level, and the presence of a total hip arthroplasty (THA) on the contralateral side did not present statistical significance. The median angle of the inclination of the acetabular component (IA) was 42.3° (range: 28.7°-52.2°). Ninety-one patients were within the defined safe range. The hit ratio for the cup to be within the safe zone was significantly higher for the Pinnacle cups than that for the Continuum cups (P < 0.05). However, there was no significant difference in gender, ASA classification, the surgeon's experience level, and the presence of a total hip arthroplasty (THA) on the contralateral side. The median of its anteversion (AA) was 20.6° (range: 10.6°-40.1°). Only 41 patients were within the defined safe range. None of the co-variables presented a statistical significance affecting the AA of the cup positioning. Meanwhile, the average fluoroscopy time for the cup positioning (n = 86, missing data in 10 cases) was 4 seconds (range: 1-74), with most of the patients (97.9%) having a fluoroscopy time of fewer than 20 seconds.

CONCLUSIONS

The combination of correct preoperative planning and standardized intraoperative measurements can reestablish right leg length and assure the correct cup positioning.