Hip surgeons and leg length inequality after primary hip replacement

Extended offset stems are infrequently required in anterior approach total hip arthroplasty and low usage does not compromise stability

INTRODUCTION

Extended offset (EO) stems are commonly used in posterior approach (PA) total hip arthroplasty (THA), but usage rates and complications are not well studied with anterior approach (AA) THA. This study evaluated usage rates, radiographic outcomes and complications following AA THA between patients receiving EO stems and a matched cohort receiving standard offset (SO) stems.

MATERIALS AND METHODS

This retrospective review evaluated 1515 consecutive AA THA performed between 2014 and 2021. The recent 100 EO were included in radiographic and complication analysis and were matched to 100 SO stems based on stem size, procedure (unilateral/bilateral), sex, body mass index (BMI), and age. Data collection included patient demographics; pre- and postoperative radiographic measurements of leg length difference (LLD) and global hip offset difference (GHOD); and complications within 1 year. Independent t-tests and Chi-squared analyses compared EO and SO groups.

RESULTS

EO was utilized in 8% of all AA THA. Despite matching procedures, the distribution of racial groups was different between EO and SO groups, respectively: Caucasian (75% vs. 43%), Asian (12% vs. 35%), Native Hawaiian/Pacific Islander (NHPI) (9% vs. 13%), and other (4% vs. 9%) (p < 0.001). No fractures, dislocations, or revisions occurred within 1 year after surgery in either group. One deep infection was noted in the SO group. The proportions of patients following surgery who had a GHOD < 6 mm (76% vs. 82%; p = 0.193) and LLD < 6 mm (81% vs. 86%; p = 0.223) were not significantly different between EO and SO groups, respectively.

CONCLUSIONS

Prioritizing hip symmetry over stability results in a high proportion of patients achieving hip symmetry without high usage of EO stems in AA THA. Furthermore, low use of EO stems did not result in increased dislocations. Due to racial anatomical differences, Caucasian patients required EO stems to achieve hip symmetry more frequently than Asian and NHPI patients.

Radiographic measurement of leg-length change in the nonoperative leg during total hip arthroplasty: a potential indicator of imaging error?

BACKGROUND

Anteroposterior (AP) pelvic radiographs are subject to errors that may cause measurement inaccuracy in total hip arthroplasty (THA). Such errors may be detected by measuring pre- to postoperative leg-length changes in the nonoperative leg, which experiences no physical changes during THA.

METHODS

From AP pelvic radiographs, we measured pre- to postoperative leg-length changes (LLC) in the nonoperative legs of 67 patients who underwent primary THA using the trans-ischial line method.

RESULTS

An LLC of 0 mm was observed in the nonoperative leg in only 14 cases (21%). A LLC ⩾ 2 mm was observed in 27% (18/67) of cases, including 13% (9/67) with LLC ⩾ 3 mm and 6% (4/67) with LLC ⩾ 4 mm. A post-hoc analysis used a validated method to measure change in pelvic tilt between pre- and postoperative images and found that changes in pelvic tilt ⩾ 4° in the anterior and posterior directions created apparent lengthening (2.0 ± 1.4 mm, p < 0.001 vs. 0-3° of tilt) and shortening (-2.1 ± 1.6 mm, p < 0.001 vs. 0-3° of tilt) of the nonoperative leg, respectively.

CONCLUSIONS

The current study provides evidence of measurement errors in leg length using AP pelvic radiographs following THA. Changes in pelvic tilt may be in part responsible for these errors, with the direction of change in pelvic tilt influencing the apparent lengthening or shortening of the lower limb. Ultimately, these findings may influence the radiographic measurement and interpretation of leg-length changes following THA.

Perioperative management of leg-length discrepancy in total hip arthroplasty: a review

Leg-length discrepancy (LLD) presents a significant management challenge to orthopedic surgeons and remains a leading cause of patient dissatisfaction and litigation after total hip arthroplasty (THA). Over or under-lengthening of the operative extremity has been shown to have inferior outcomes, such as dislocation, exacerbation of back pain and sciatica, and general dissatisfaction postoperatively. The management of LLD in the setting of THA is multifactorial, and must be taken into consideration in the pre-operative, intra-operative, and post-operative settings. In our review, we aim to summarize the best available practices and techniques for minimizing LLD through each of these phases of care. Pre-operatively, we provide an overview of the appropriate radiographic studies to be obtained and their interpretation, as well as considerations to be made when templating. Intra-operatively, we discuss several techniques for the assessment of limb length in real time, and post-operatively, we discuss both operative and non-operative management of LLD. By providing a summary of the best available practices and strategies for mitigating the impact of a perceived LLD in the setting of THA, we hope to maximize the potential for an excellent surgical and clinical outcome.

Using a ring to locate femoral head centre in total hip arthroplasty

AIMS

Traditional methods of determining femoral head centre (FHC) during total hip arthroplasty (THA) rely on measuring the distance from a fixed point on the femur or using a calliper. The aim of this experiment was to investigate how accurately a simple circular ring could locate FHC.

METHODS

144 consecutively available femoral heads (FHs) were collected from patients undergoing THA. Each FH was orientated and mounted on a Sawbone, to create a model of its position on a proximal femur. The ring was applied to the posterior aspect of the FH and a head-centre pin (HCP) was then drilled into the FH and the ring removed, leaving the HCP in place.Each FH was then photographed normal to the axis of the HCP. A MATLAB analysis program then assessed the accuracy of the ring in locating FHC.

RESULTS

Mean location accuracy for FHC was 1.77 (range 0.07-5.83) mm with 97.2% within 4 mm and all but 1 within 5 mm.

CONCLUSIONS

This ring device located FHC to within 4 mm in 97% of a series of osteoarthritic FHs. This indicates that the posterior aspect of the FH maintains its sphericity late into the osteoarthritic process. Having a simple FHC location device during THA would be of value to control leg length and offset when using the posterior approach.

Limb Length Inequality in Patients After Primary Total Hip Arthroplasty: Analysis of Radiological Assessment and Influencing Risk Factors Based on a District General Hospital Experience of 338 Cases

Background and objective

Limb length inequality (LLI) is a frequent and recurring issue after total hip arthroplasty (THA). It is often a source of patient dissatisfaction and litigation. This study reviewed the incidence of LLI in a UK District General Hospital in light of published evidence and identified the preoperative and intraoperative risk factors for LLI.

Methods

This was a retrospective study involving 380 consecutive unilateral primary total hip replacements over a period of 12 months. Patient demographics, clinical, radiological, and operative details were collected from the National Joint Registry (NJR) database and hospital records. The limb length was measured radiologically [OrthoView Workstation^TM (Materialise UK, Southampton, UK)], pre- and postoperatively, by two authors. They assessed the vertical distance between the intra-acetabular teardrop line and the medial apex of the lesser trochanters. After excluding complex primary, revision cases, tilted X-rays, and hip replacement for trauma patients, 338 cases were included in the final analysis.

Results

The mean postoperative LLI was 2.7 mm with a standard deviation (SD) of 6.56 mm. Only 5.3% of patients had LLI >15 mm. None of the studied variables showed a statistically significant correlation with LLI. Even with the apparent difference in the mean LLI between templating and not templating before surgery (2.19 vs. 3.53), the p-value was 0.06, which was below the level of statistical significance. There was a weakly positive Pearson correlation between body mass index (BMI) and the incidence of lengthening of the limb.

Conclusion

The cause of LLI after THA is multifactorial. No single factor can be singled out as the most significant contributor to this complication.

Reliability of a simple fluoroscopic image to assess leg length discrepancy during direct anterior approach total hip arthroplasty

BACKGROUND

Direct anterior approach (DAA) total hip arthroplasty (THA) in a supine position provides a unique opportunity to assess leg length discrepancy (LLD) intra-operatively with fluoroscopy. Reported fluoroscopic techniques are useful but are generally complicated or costly. Despite the use of multiple techniques for leg length assessment, LLD continues to be a major post-operative source of patient dissatisfaction further emphasizing the importance of near-anatomic restoration. The utility of an alternative direct measurement of LLD on an intra-operative fluoroscopic pelvic image during DAA THA has not been reported.

AIM

To determine the reliability of a novel simple intra-operative measurement of LLD using a parallel line technique on a single fluoroscopic digital image of the pelvis.

METHODS

One hundred and seventy-one patients who underwent DAA THA were included for analysis. Intra-operative fluoroscopic and post-operative anterior-posterior radiographs were imported to TraumaCad and calibrated for LLD measurement. LLD was measured on each image using the right-left hip differences in lesser trochanter to pelvic reference line distances. Pelvic reference points included the teardrops and ischia. Fluoroscopic LLD was compared to the gold-standard measurement of LLD measured on a post-operative radiograph.

RESULTS

Mean absolute difference in teardrop referenced LLD between fluoroscopic and post-operative radiographs was 2.17 mm and based on the ischia mean absolute difference was 2.63 mm. Linear regression of fluoroscopic and post-operative radiograph LLD based on teardrop and ischia LLD found r² values of 0.57 and 0.84, respectively. Mean absolute difference between fluoroscopic and post-operative x-ray LLD was within 5 mm in 95% of cases regardless of pelvic reference.

CONCLUSION

This study demonstrates that a single fluoroscopic view obtained during DAA THA for leg length assessment is clinically useful.

The External Obturator Footprint Is a Usable, Accurate, and Reliable Landmark for Stem Depth in Direct Anterior THA

BACKGROUND

Previous CT and cadaver studies have suggested that the external obturator footprint might be used as a landmark for stem depth in direct anterior THA. Instructions on where to template this structure with small variability in height have been developed but have not been tested in daily clinical practice.

QUESTIONS/PURPOSES

In this study we sought to investigate the (1) usability, (2) accuracy, and (3) reliability of the external obturator footprint as a landmark for stem depth in direct anterior THA.

METHODS

The distance between the superior border of the external obturator tendon and the shoulder of the stem was measured intraoperatively in all patients (n = 135) who underwent primary THA via a direct anterior approach performed by the senior author between November 2019 and October 2020. The landmark was considered useful when two of thre`e evaluators agreed that the intersection of the vertical line comprised of the lateral wall of the trochanteric fossa and the oblique line formed by the intertrochanteric crest was clearly visible on the preoperative planning radiograph, and when the landmark was furthermore identified with certainty during surgery. Accuracy was defined as the degree of agreement (categorical for thresholds of 2 and 5 mm, the latter representing the threshold for developing unphysiological gait parameters) between the intraoperative distance and radiographic distance as measured on intraoperative fluoroscopy images or postoperative radiographs, which were calibrated based on femoral head sizes in a software program commonly used for templating. Intrarater reliability was defined as the degree of agreement (categorical for thresholds of 1 mm, which we considered an acceptable measurement error) between the ratings of one observer, who measured the radiographic distance on two different occasions separated by a washout period of at least 2 weeks. Interrater reliability was defined as the degree of agreement (categorical for thresholds of 1 mm, which we considered an acceptable measurement error) between the ratings of three observers with varying levels of experience (a fellowship-trained hip surgeon, a hip surgery fellow, and a medical student).

RESULTS

The landmark was considered useful in 77% (104 of 135) of patients who underwent direct anterior THA based on the observations that the trochanteric fossa was clearly visible on the planning radiograph in 117 patients and that the tendon was identified with certainty during surgery in 118 patients. There was good-to-excellent accuracy (intraclass correlation coefficient 0.75-087), and intrarater reliability (ICC 0.99) and interrater reliability (ICC 0.99) were both excellent.

CONCLUSION

This clinical study showed that the external obturator footprint is a useful, accurate, and reliable landmark for stem depth in direct anterior THA.

CLINICAL RELEVANCE

The external obturator landmark allows the surgeon to position the stem within a range of the templated depth that is beneath the threshold for the development of unphysiological gait parameters. Although strictly speaking it was found useful in 77% of patients in this study, we found that this percentage of usability can easily be improved to around 90% by providing the radiology lab technician with instructions to correct external rotation of the foot during the taking of the planning radiograph. Future studies could compare the established (in)equality in leg length in patients using the external obturator landmark with computer-assisted surgery.

Anatomical Mapping of the External Obturator Footprint: A Study In Cadavers with Implications for Direct Anterior THA

BACKGROUND

The external obturator footprint in the trochanteric fossa has been suggested as a potential landmark for stem depth in direct anterior THA. Its upper border can be visualized during surgical exposure of the femur. A recent study reported that the height of the tendon has little variability (6.4 ± 1.4 mm) as measured on CT scans and that the trochanteric fossa is consistently visible on conventional pelvic radiographs. However, it is unclear where exactly the footprint of this tendon should be templated during preoperative planning so that it can be useful intraoperatively.

QUESTIONS/PURPOSES

In this study, we sought: (1) to provide instructions on exactly where to template the external obturator footprint on a preoperative planning radiograph, and (2) to confirm the small variability in height of the external obturator footprint found on CT scans in a cadaver study.

METHODS

Two-dimensional (2-D) and three-dimensional (3-D) imaging was used to map the anatomy of the external obturator footprint. This dual approach was chosen because of their complementarity; conventional 2-D radiographs translate to clinical practice but 3-D navigation-based digitalization combined with CT allows for a better understanding of the cortical lines that comprise the outline of the trochanteric fossa. In 12 (four males, mean age 80 years, range 69 to 88) formalin-treated cadaveric lower extremities including the pelvis, the external obturator tendon was dissected, and the top and bottom end of its footprint marked with two small needles, and calibrated radiographs were taken. For another five (three males, mean age 75.7 years, range 61 to 91) fresh-frozen cadaveric lower extremities, including femoral reflective marker frames, CT scans were obtained and the exact location of the external obturator footprint was recorded using 3-D navigation-based digitalization. Qualitative analysis of both imaging modalities was used to develop instructions on where the external obturator footprint should be templated on a preoperative planning radiograph. Quantitative analysis of the dimensions of the external obturator footprint was performed.

RESULTS

The lowest point of the external obturator footprint was consistently found (± 1 mm) at the intersection of the vertical line comprised of the lateral wall of the trochanteric fossa and the oblique line formed by the intertrochanteric crest and therefore allows templating of this structure on the preoperative planning radiograph. The median (range) height of the footprint measured 6.4 mm and demonstrated small variability (4.7 to 7.6).

CONCLUSIONS

We suggest templating a 6.4-mm circle with its bottom on the intersection described above.

CLINICAL RELEVANCE

The distance between the templated shoulder of the stem and the top of the circle can be used intraoperatively for guidance. Discrepancy should lead to re-evaluation of stem depth and leg length. Future work will investigate the usability, validity, and reliability of the proposed methodology in daily clinical practice.

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