Limb Length Discrepancy in Total Hip Arthroplasty: Is the Lesser Trochanter a Reliable Measure of Leg Length?

Leg Length Discrepancy in Total Hip Arthroplasty: Not All Discrepancies Are Created Equal

The original review article, published in 2006, describing leg length discrepancy after total hip arthroplasty commented that "equal leg length should not be guaranteed." There has been considerable advancement in surgical technique and technology over the past decade, allowing surgeons to "hit the target" much more consistently. In this interval paper, we review leg length discrepancy and introduce some technologies designed to mitigate this complication. In addition, we present challenging clinical scenarios in which perceived leg length may differ from true leg length and how these can be addressed with proper workup and surgical execution.

What is the clinical detection threshold for lower limb length inequality? In silico study of reproducibility and optimization using a centimeter graduated support

INTRODUCTION

The threshold of a Leg Length Discrepancy (LLD) by clinical examination on a sheet or centimeter paper (CP) is not known precisely whether or not it concerns limbs equipped with a hip prosthesis. We therefore conducted a prospective in silico study in order to: (1) determine the reproducibility and sensitivity of the clinical measurement of the LLD in different ideal and "degraded" clinical situations, (2) determine the threshold from which the human eye is capable of detecting a length inequality in clinic, (3) to determine whether the use of a graduated support (centimeter paper) improves the clinical measurement threshold.

HYPOTHESIS

Our hypothesis was that clinical measurement on a centimeter support would improve clinical measurement accuracy.

MATERIAL AND METHODS

This was an in silico study, the experiment was conducted on a mannequin. Different inequalities were created on a mannequin and photographed with a total of 30 inequalities from -22 to +22 mm on sheet or centimeter paper (CP). This was a multicenter study, with 40 different readers. We asked the readers to make a second measurement one month later. We evaluated the inter- and intra-observer reproducibility. The error rate at the threshold of 3 mm and 5 mm were calculated versus the gold standard. Finally, we determined at which thresholds respectively 75% and 95% of the measurements were correct.

RESULTS

A total of 4140 measurements were performed and compared to the gold standard. With a threshold of 75% accurate measurement, the LLD detection threshold was 2.8 mm on centimeter paper and 4.5 mm on sheet. With a threshold of 95% accurate measurement, the LLD detection threshold was 3.4 mm on centimeter paper and 5.2 mm on sheet. Interobserver agreement (assessed overall on the 40 observers by Krippendorff's generalized Kappa) was 0.86 (95% confidence interval (CI95%) = 0.79 to 0.92) on CP and 0.71 (CI95% = 0.63 to 0.79) on sheet. Intra-observer agreement assessed by the intraclass correlation coefficient among observers who made 2 measurements had a median value (IQR) of 0.96 (0.94 to 0.99) on CP and 0.90 (0.83 to 0.94) on sheet.

DISCUSSION

The clinical detection threshold on sheet at the patient's bed appears close to 5 mm. A more precise measurement is possible with graduated centimeter paper. A study in daily practice on patients in real situations would confirm our results.

LEVEL OF EVIDENCE

III; prospective diagnostic comparative in Silico study.

Comparative Study of Alternative Methods for Measuring Leg Length Discrepancy after Robot-Assisted Total Hip Arthroplasty

BACKGROUND

Our study addresses the lack of consensus on measuring leg length discrepancy (LLD) after total hip arthroplasty (THA). We will assess the inter-observer variability and correlation between the five most commonly used LLD methods and investigate the use of trigonometric principles in overcoming the limitations of current techniques.

METHODS

LLD was measured on postoperative AP pelvic radiographs using five conventional methods. CT images created a 3D computer model of the pelvis and femur. The resulting models were projected onto a 2D, used to measure LLD by the five methods. The measurements were evaluated via Taguchi analysis, a statistical method identifying the process's most influential factors. The approach was used to assess the new trigonometric method.

RESULTS

Conventional methods demonstrated poor correlation. Methods referenced to the centers of the femoral heads were insensitive to LLD originating outside the acetabular cup. Methods referencing either the inter-ischial line or the inter-obturator foramina to the lesser trochanter were sensitive to acetabular and femoral components. Trigonometry-based measurements showed a higher correlation.

CONCLUSIONS

Our results underscore clinicians' need to specify the methods used to assess LLD. Applying trigonometric principles was shown to be accurate and reliable, but it was contingent on proper radiographic alignment.

Restoration of hip anatomy using computer modelling prior to total hip arthroplasty and its potential consequences in terms of lower limb-length difference

BACKGROUND

Restoring hip anatomy during total hip arthroplasty (THA) is the gold standard. The general goal is for hips to be symmetrical in terms of height. This study aimed to analyse the effect of simulating hip length (HL) equalisation on leg-length difference (LLD) before and after THA with a computerised plan.

METHODS

141 consecutive patients were enrolled following THA. Outcomes of interest were preoperative hip-length difference (HLD) and LLD as determined on CT and final LLD as determined by simulating HL equalisation. We divided patients into 3 groups: no LLD, LLD >5 mm and LLD ⩾10 mm.

RESULTS

The rate of preoperative LLD >5 mm and LLD ⩾10 mm was 37.5% and 14.8%, respectively. HL equalisation did not change LLD distribution in the overall cohort. Among patients with smaller preoperative HLs and LLDs, HL equalisation changed the rate of LLD >5 mm from 100% (n = 24) to 41.7% (n = 10) (p < 0.0001) and of LLD ⩾10 mm from 100% (n = 12) to 16.7% (n = 2) (p < 0.0001). Among patients with no preoperative LLD, HL equalisation changed the rate of LLD ⩽5 mm from 100% (n = 64) to 59.3% (n = 38) (p < 0.0001) and of LLD<10 mm from 100% (n = 76) to 89.5% (n = 68) (p = 0.006).

CONCLUSIONS

Restoring biomechanical hip anatomy by HL equalisation may not be the correct goal for all patients. In patients with no LLD and shorter HLs, equalisation could result in LLD >5 mm in 40% of patients and LLD >10 mm in 10%, demonstrating the necessity to further analyse individuals and propose a personalised stem position.

Leg-Length Discrepancy Variability on Standard Anteroposterior Pelvis Radiographs: An Analysis Using Deep Learning Measurements

BACKGROUND

Leg-length discrepancy (LLD) is a critical factor in component selection and placement for total hip arthroplasty. However, LLD radiographic measurements are subject to variation based on the femoral/pelvic landmarks chosen. This study leveraged deep learning (DL) to automate LLD measurements on pelvis radiographs and compared LLD based on several anatomically distinct landmarks.

METHODS

Patients who had baseline anteroposterior pelvis radiographs from the Osteoarthritis Initiative were included. A DL algorithm was created to identify LLD-relevant landmarks (ie, teardrop (TD), obturator foramen, ischial tuberosity, greater and lesser trochanters) and measure LLD accurately using six landmark combinations. The algorithm was then applied to automate LLD measurements in the entire cohort of patients. Interclass correlation coefficients (ICC) were calculated to assess agreement between different LLD methods.

RESULTS

The DL algorithm measurements were first validated in an independent cohort for all six LLD methods (ICC = 0.73-0.98). Images from 3,689 patients (22,134 LLD measurements) were measured in 133 minutes. When using the TD and lesser trochanter landmarks as the standard LLD method, only measuring LLD using the TD and greater trochanter conferred acceptable agreement (ICC = 0.72). When comparing all six LLD methods for agreement, no combination had an ICC>0.90. Only two (13%) combinations had an ICC>0.75 and eight (53%) combinations had a poor ICC (<0.50).

CONCLUSION

We leveraged DL to automate LLD measurements in a large patient cohort and found considerable variation in LLD based on the pelvic/femoral landmark selection. This emphasizes the need for the standardization of landmarks for both research and surgical planning.

Robotic arm-assisted total hip arthroplasty for preoperative planning and intraoperative decision-making

AIMS

This article aimed to explore the efficacy of robotic arm-assisted total hip arthroplasty (THA) in improving preoperative planning and intraoperative decision-making.

METHODS

In this single-center, prospective, randomized clinical controlled trial, 60 patients were randomly divided into two groups: conventional THA (cTHA) and robotic arm-assisted THA (rTHA). The rTHA underwent procedures using a robot-assisted surgical system, which generated three-dimensional models to determine the most appropriate prosthesis size and position. The standard process of replacement was executed in cTHA planned preoperatively via X-ray by experienced surgeons. Differences between predicted and actual prosthetic size, prosthetic position, and leg length were evaluated.

RESULTS

Sixty patients were included in the study, but one patient was not allocated due to anemia. No significant preoperative baseline data difference was found between the two groups. The actual versus predicted implantation size of both groups revealed that 27/30 (90.0%) in the rTHA group and 25/29 (86.2%) in the cTHA group experienced complete coincidence. The coincidence rate for the femoral stem was higher in the rTHA group (83.3%) than that in the cTHA group (62.7%). Between the actual and predicted rTHA, the difference in anteversion/inclination degree (< 6°) was largely dispersed, while cTHA was more evenly distributed in degree (< 9°). The differences in leg length between the surgical side and contralateral side showed a significant deviation when comparing the two groups (P = 0.003), with 0.281 (- 4.17 to 3.32) mm in rTHA and 3.79 (1.45-6.42) mm in cTHA.

CONCLUSION

Robotic arm-assisted total hip arthroplasty can be valuable for preoperative planning and intraoperative decision-making.

Does the use of intraoperative measurement reduce limb length discrepancies after total hip arthroplasty?

PURPOSE

Postoperative limb length discrepancy (LLD) is a common complication of total hip arthroplasty, and several methods exist to prevent LLD, but each has its benefits and drawbacks. The study investigates the application of intraoperative lower limb length measurement in preventing postoperative LLD.

METHODS

This study retrospectively analyzed 70 patients who underwent total hip arthroplasty from October 2018 to July 2022. The length of the lower limb on the operated side was measured intraoperatively using a sterilized paper ruler after the fitting of the trial mould and compared with the healthy side. Then the prosthesis size, depth and neck length were adjusted accordingly.

RESULTS

The absolute value of postoperative LLD was found to be 6.68 ± 4.48 mm, of which 53 cases (75.7%) were less than or equal to 10 mm, while 30 patients (42.9%) were less than or equal to 5 mm.

CONCLUSION

The use of intraoperative measurement is effective in reducing LLD after total hip arthroplasty.

An Analysis of Radiographic Leg Length Discrepancy and Hip Offset in Patients at Risk of Developing Osteoarthritis

Background

Leg length and hip offset are important principles in total hip arthroplasty (THA). Patients may endorse leg length differences (LLD) postoperatively that may be anatomical or functional. The objective of this study was to determine the normal radiographic variation in leg length and hip offset in a preosteoarthritic population without a THA.

Methods

A retrospective study was completed using data from the Osteoarthritis Initiative, a prospective longitudinal study. Patients at risk of developing or with early osteoarthritis without inflammatory arthritis or prior THA were included. Measurements were made from full limb length anterior-posterior (AP) radiographs. Multiple linear regression models were employed to predict side-to-side differences in LLD, Δ femoral offset (FO), Δ abductor muscle length (AML), Δ abductor lever arm, and Δ AP pelvic offset.

Results

The mean radiographic LLD was 4.6 mm, with 12 mm within 1 standard deviation. No significant differences were detected between LLD and sex, age, body mass index, or height. The median radiographic differences in FO, AML, abductor lever arm, and AP pelvic offset were 3.2 mm, 4.8 mm, 3.6 mm, and 3.3 mm, respectively. Height was predictive of Δ FO, while both height and age were predictive of Δ AML.

Conclusions

Radiographic leg length variations in a population without symptomatic or radiographic osteoarthritis exist. FO and AML are dependent on patient characteristics. Preoperative radiographic LLD is not predicted by age, gender, body mass index, or height. It should be stressed that anatomic reconstruction is one of the many goals of arthroplasty and can stand in conflict with the priority and primary goals of stability and fixation, which should be prioritized.

Leg Length Discrepancy After Hip Fracture Repair is Associated With Reduced Gait Speed

Introduction

A negative correlation exists between functional outcomes and leg length discrepancy (LLD) following hip fracture repair. We have assessed the effects of LLD following hip fracture repair in elderly patients on 3-meter walking time, standing time, activities of daily living (ADL), and instrumental activities of daily living (IADL).

Methods

One hundred sixty-nine patients enrolled in the STRIDE trial were identified with femoral neck, intertrochanteric, and subtrochanteric fractures that were treated with partial hip replacement, total hip replacement, cannulated screws, or intramedullary nail. Baseline patient characteristics recorded included age, sex, body mass index Charlson comorbidity index (CCI) score. ADL, IADL, grip strength, sit-to-stand time, 3-meter walking time and return to ambulation status were measured at 1 year after surgery. LLD was measured on final follow-up radiographs by either the sliding screw telescoping distance or the difference from a trans-ischial line to the lesser trochanters, and was analyzed as a continuous variable using regression analysis.

Results

Eighty eight patients (52%) had LLD <5 mm, 55 (33%) between 5-10 mm and 26 subjects (15%) >10 mm. Age, sex, BMI, Charlson score, and ambulation status had no significant impact on LLD occurrence. Type of procedure and fracture type did not correlate with severity of LLD. Having a larger LLD was not found to have a significant impact on post-operative ADL (P = .60), IADL (P = .08), sit-to-stand time (P = .90), grip strength (P = .14) and return to former ambulation status (P = .60), but did have a statistically significant impact on 3-meter walking time (P = .006).

Discussion

LLD after hip fracture was associated with reduced gait speed but did not affect many parameters associated with recovery. Continued efforts to restore leg length after hip fracture repair are likely to be beneficial.

Factors influencing inconsistent leg length discrepancy in dysplastic hip osteoarthritis: a retrospective study

BACKGROUND

We aimed to examine the inconsistency between radiographic leg length discrepancy (R-LLD) and perceived LLD (P-LLD) in patients with dysplastic hip osteoarthritis and to evaluate the factors that can cause such inconsistency.

METHODS

We conducted a retrospective study on 120 patients. An inconsistent LLD was defined as a condition in which the P-LLD was shorter than the R-LLD by > 5 mm. We compared relevant data on the general characteristics of the patients and the radiological findings between consistent (group E, 92 cases [76.7%]) and inconsistent LLDs (group S, 28 cases [23.3%]).

RESULTS

The number of patients with a history of hip surgery on the affected side and the Japanese Orthopedic Association classification pain scores were significantly higher in group S than in group E (32.1% vs. 10.8%, respectively; P = 0.015, and 21.7 ± 7.0 vs. 17.5 ± 8.2, respectively; P = 0.036). The pelvic oblique angle and length of the R-LLD were significantly higher in group S than in group E (2.9 ± 2.5° vs. 0.3 ± 2.3°, respectively; P < 0.01, and 17.2 ± 8.9 mm vs. 6.3 ± 8.4 mm, respectively; P < 0.01). Multivariate logistic analysis revealed that the pelvic oblique angle (odds ratio [OR]: 1.80, 95% confidence interval [CI]: 1.28-2.52; P < 0.01) and length of the R-LLD (OR: 2.75, 95% CI: 1.24-6.12; P = 0.013) were independent risk factors of inconsistent LLD.

CONCLUSION

The pelvic oblique angle and a long R-LLD were independent risk factors of inconsistent LLD in patients with dysplastic hip osteoarthritis. Therefore, hip surgeons should consider P-LLD rather than R-LLD to understand the need for conservative intervention.

Stem Geometry Recommendation for Total Hip Replacement Planning Using Computed Tomography Data Analysis

Total Hip Replacement (THR) requires careful planning preparation, especially in the geometry suitability between the patient's bone and the implant. If it is applied incorrectly, it will be dangerous for the patient, such as the risk of complications, dislocation, and re-surgery. This paper aims to compare the size of the patient's THR geometry as a basis for consideration in implant designs to minimize the risk of harm after implantation. This study was limited to male patients only. The computed tomography scanning data (CT-Scan data) in the lower abdomen, segmented to hip joint area belonging to the American race and an Indonesian male, were compared. The comparison indicates that the American race data has a greater dimension than Indonesian. The American hip bone geometry result is following the standard modern implant by Johnson and Johnson size. By all analysis, the fittest geometry for the Indonesian male patient needs to adjust and has a smaller size than the commercial implant. This study finally recommends the specific length of the femoral stem for the optimal THR implant with the parameter values of Femoral Head Offset, Neck Length, Neck Shaft Angle, Mediolateral Width 1, Mediolateral Width 2, Mediolateral Width 3 respectively for the right THR, namely 37.9; 31.6; 134.3; 43.1; 13.62; 12.36; while the left THR is 38.9; 31.7; 134.5; 43.1; 13.70; 12.4 in mm. Overall, the precise implant planning based on real patient conditions and anthropometry is necessary to match implants and bone anatomy.