Evaluating the Reliability of the Lesser Trochanter as a Landmark for Limb Length Discrepancy in Direct Anterior Approach Total Hip Arthroplasty

Abstract

Background and aim Limb length discrepancy (LLD) is a common complication following total hip arthroplasty (THA), significantly impacting functional outcomes, patient satisfaction, and quality of life. The direct anterior approach (DAA) for THA has gained popularity due to its potential for minimizing LLD through precise intraoperative control. Despite advancements, achieving limb length equality remains challenging, particularly in the Indian patient population, where anatomical variations may affect surgical outcomes. The lesser trochanter (LT) is frequently utilized as a landmark for intraoperative LLD assessment. However, the reliability of the LT in DAA-THA remains debated. This study aimed to evaluate the accuracy and consistency of using the LT as an intraoperative reference for LLD correction in DAA-THA. Methods A retrospective cohort analysis was conducted on 130 patients who underwent DAA-THA at a high-volume tertiary care center between January 2023 and December 2023. Patients were selected based on the inclusion criteria of age >18 years, availability of preoperative and postoperative radiographs, and adequate fluoroscopic imaging during surgery. The LT was used as the primary landmark for limb length restoration. Intraoperative fluoroscopy and standardized leg positioning systems were employed to ensure accurate component placement. Preoperative and postoperative LLD were measured using standardized radiographic techniques, and functional outcomes were assessed through the Harris Hip Score (HHS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Forgotten Joint Score (FJS). Statistical analysis was performed to determine the association between LLD correction and functional recovery. Results The cohort had a mean age of 57.1 years, with 70% males and 30% females. The mean BMI was 27.1 ± 4.4 kg/m². Primary indications were avascular necrosis (73.8%), femoral neck fractures (19.2%), rheumatoid arthritis (6.2%), and primary osteoarthritis (0.8%). The mean preoperative LLD of 1.5 cm was reduced to 0.2 cm postoperatively, with only two patients having LLD >1 cm. Functional outcomes improved significantly postoperatively, with HHS increasing from 40.7 ± 5.7 preoperatively to 95.1 ± 4.4 at 12 months (p < 0.001). The WOMAC score decreased from 60.7 ± 5.8 to 10.1 ± 6.7 over the same period (p < 0.001). The FJS improved from 19.9 ± 6.45 preoperatively to 85.5 ± 9.3 postoperatively, indicating high patient satisfaction. Patients with postoperative LLD ≤0.5 cm had significantly higher HHS and lower WOMAC scores compared to those with residual LLD >1 cm, highlighting the importance of precise LLD correction for optimal functional recovery. Conclusion The LT serves as a reliable anatomical landmark for correcting LLD during DAA-THA, particularly when combined with intraoperative fluoroscopy and standardized positioning systems. This approach resulted in favorable postoperative functional outcomes and high patient satisfaction. Implementing standardized protocols that include LT-based measurements and fluoroscopic validation can significantly reduce LLD, enhancing clinical outcomes in THA. Further research is warranted to validate these findings in larger, multicenter cohorts.

Keywords: direct anterior approach; fluoroscopic validation; functional outcomes; lesser trochanter (lt); limb length discrepancy; total hip arthroplasty.

Figure 1. Limb length discrepancy after direct anterior approach total hip arthroplasty (in cm).

Figure 2. Radiographic assessment and intraoperative technique in direct anterior approach bilateral total hip arthroplasty (THA).

Panel A: Preoperative radiograph of a 63-year-old patient with bilateral avascular necrosis (AVN) of the femoral head. Neither the patient nor the surgeon identified any actual or perceived limb length discrepancy (orange arrow). The patient underwent single-stage bilateral THA. Panel B: Intraoperative fluoroscopic images during left THA, utilizing the lesser trochanter (red curved lines) as an anatomical landmark for limb length assessment during a single-stage bilateral THA. Panel C: Immediate postoperative radiograph demonstrating the achieved leg length equality, confirming the accuracy of intraoperative limb length restoration (yellow arrow).

Figure 3. Radiographic evaluation of limb length discrepancy (LLD) following direct anterior approach total hip arthroplasty

Panel A: Preoperative anteroposterior pelvic radiograph of a patient with significant limb length discrepancy (LLD, 2.6 cm) due to advanced hip pathology. The yellow reference line indicates the baseline limb length difference, and red curved lines show the difference in lesser trochanter position. Panel B: Immediate postoperative radiograph after total hip arthroplasty via the direct anterior approach showing partially corrected LLD to 1.5 cm postoperatively (yellow line) with the hip in a neutral position, with the lesser trochanter (red curved lines) as a point of reference.

Figure 4. Harris Hip Score in patients undergoing direct anterior approach total hip arthroplasty.

Figure 5. WOMAC scores in patients undergoing direct anterior approach total hip arthroplasty.

WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index

Figure 6. Forgotten joint score in patients undergoing direct anterior approach total hip arthroplasty.