Birmingham Royal Orthopaedic Hospital (BROH) Femoral Offset-An Ancillary Measure of Adult Dysplasia of the Hip

Introduction  Adult dysplasia of the hip (ADH) is a disorder of abnormal development of the hip joint resulting in a shallow acetabulum and uncovering of the femoral head. Several radiological measurements such as the Tönnis angle (acetabular index), lateral center edge angle of Wiberg, and cross-sectional imaging parameters exist to calculate hip dysplasia. Aims  The aim of this article was to describe a new ancillary linear measure of ADH on cross-sectional imaging, the Birmingham Royal Orthopaedic Hospital (BROH) Femoral offset. Patients and Methods  Anteroposterior radiographs of the pelvis and computed tomography imaging of 100 consecutive patients with suspected hip dysplasia were reviewed. Demographic details and clinical indications were recorded. Tönnis angle was utilized to measure hip slope on radiographs and the BROH femoral offset was calculated for each patient. Student's t -test and one-way analysis of variance (ANOVA) were performed. Intraclass correlation coefficient analysis was evaluated to assess the reliability between observers. Results  There was a total of 100 patients (128 hips) included in the study (60 with normal Tönnis angle, 53 had dysplasia, and 15 had decreased Tönnis angle). The average BROH femoral offset in the dysplastic cohort was increased in comparison to the normal cohort with a statistically significant p -Value of 0.0001. The p -value was 0.00031 on ANOVA. The BROH femoral offset calculation revealed good intra- and interobserver reliability of 0.9 and 0.9, respectively. Conclusion  The BROH femoral offset can be an additional index for measuring ADH that is easier to calculate, and reproducible with good intra- and inter-observer reliability on cross-sectional imaging.

Tönnis angle and acetabular depth ratio: predictors of dislocation following hemiarthroplasty for hip fracture

BACKGROUND

Despite efforts to mitigate possible modifiable risk factors, dislocations following hemiarthroplasty for hip fracture still occur, with reported incidence rates ranging from 1.5 to 11%. The aim of this study was to investigate whether acetabular dysplasia is a significant contributing factor to dislocation, and since non-modifiable, whether it should affect patient selection for this treatment option.

METHODS

This is a multicentre nested case-control study of patients treated at 2 separate centres over a 10-year period from January 2011 to December 2020. All cases of hemiarthroplasty dislocation following hip fracture were identified from local databases, and 4 random controls were selected for every case. Tönnis angle (TA) and Acetabular-depth-ratio (ADR) was measured on the injured side using AP pelvis radiographs. Patients with TA > 10° and/or ADR < 250 were considered to have abnormal acetabular morphology.

RESULTS

35 cases of dislocation were identified and 140 random controls were selected. Cases of dislocation had a larger mean TA (8.8° vs. 5.5°, p < 0.001) and lower mean ADR (254 vs. 289, p < 0.001) than controls. 20 out of 35 (57%) cases were considered to have abnormal acetabular morphology, compared to 19 out of 140 (14%) controls. The odds of dislocation is 8.5 times greater (odds ratio = 8.49, 95%CI = 3.73, 19.39) in patients with abnormal TA and/or ADR.

CONCLUSIONS

This study demonstrates that TA > 10° and ADR < 250 are useful criteria to identify patients at greater risk of hip hemiarthroplasty dislocation due to acetabular dysplasia. Special consideration to preoperative planning should be taken in these patients. Future research should focus on methods to minimise risk in this subset of patients, including evaluating total hip arthroplasty with dual mobility component vs hemiarthroplasty.

Developmental dysplasia of the hip is common in patients undergoing total hip arthroplasty under 50 years of age

INTRODUCTION

Developmental dysplasia of the hip (DDH) refers to congenital and/or developmental hip instability that can result in hip joint subluxation or dislocation. When detected neonatally, conservative treatment with hip bracing can restore normal hip anatomy. Missed detection of DDH in the neonatal period or late development of DDH often requires surgical intervention to correct the abnormal anatomy. Furthermore, despite surgical intervention, residual sequelae may persist leading to early osteoarthritis of the hip joint requiring joint replacement surgery.

AIM

This study investigates the prevalence of hip dysplasia in patients undergoing total hip arthroplasty (THA) under 50 years of age.

METHODS

The hip arthroplasty database at a national referral centre was investigated from January 2014 to December 2020. In patients under 50 years of age, those with an adequate pre-operative anteroposterior pelvic radiograph without previous hip arthroplasty were included, while those with inadequate radiographs were excluded. The following measurements were made on the contralateral non-operated hip: (1) lateral centre-edge angle (LCEA), (2) Tönnis angle, (3) acetabular version, (4) acetabular depth, (5) femoral head lateralisation, (6) femoral head extrusion index, and (7) acetabular depth-to-width ratio.

RESULTS

In total, 451 patients were included in this study. Twenty two percent of the patients had hip dysplasia, based on a LCEA of <25° and 42.6% of patients had hip dysplasia, based on a Tönnis angle of > 10°. The mean LCEA and Tönnis angle were 31.47 ± 9.64 and 9.82 ± 6.79°, respectively.

CONCLUSION

Hip dysplasia is common in patients undergoing THA under the age of 50 years with over 40% having dysplasia according to the Tönnis angle. Classification of primary and secondary osteoarthritis in the joint registries will benefit our knowledge on the prevalence of DDH in the adult population.

Surgical correction for adult spinal deformity increases acetabular lateral coverage of femoral heads

BACKGROUND

Studies explaining the relationship between hip and spine reported that spinal corrective surgery affected acetabular orientation and changes in pelvic tilt were capable of influencing radiographic measures of acetabular coverage. This study aimed to assess the change in coronal parameters for acetabular coverage as a result of adult spinal deformity (ASD) correction and to analyze the relationship between the postoperative changes in sagittal spinopelvic parameters and coronal acetabular coverage parameters.

METHODS

Fifty-two consecutive patients who had undergone multilevel spinal surgical correction were enrolled and evaluated. Coronal acetabular coverage parameters included Tönnis angle (TA), lateral center edge angle (LCEA), and the angle of Sharp (SA). All radiographic parameters were evaluated at the preoperative and the postoperative 1 year. Paired t test was used to determine whether there were significant changes between the time points. Bivariate correlation and linear regression analysis were used to assess the relationship between the postoperative changes of spinal alignment and acetabular orientation.

RESULTS

The surgical correction resulted in significant decrease of TA, increase of LCEA and SA, respectively (p < 0.001). The changes in pelvic tilt (PT) demonstrated weak correlation on TA (β = 0.117, p < 0.001 for right; β = 0.111, p < 0.001 for left).

CONCLUSIONS

Although the surgical correction of ASD significantly changed PT resulting in increased acetabular lateral coverage parameters, the correlation between the changes of PT following sagittal correction of ASD and acetabular coverage parameters was low.

TRIAL REGISTRATION

This study was retrospectively registered with approval by the institutional review board (IRB) of our institution (approval number: KHNMC-2020-10-010).

A Multicenter Study of Radiographic Measures Predicting Failure of Arthroscopy in Borderline Hip Dysplasia: Beware of the Tönnis Angle

BACKGROUND

Hip arthroscopy has been previously demonstrated to be an effective treatment for adult mild hip dysplasia. There are many radiographic parameters used to classify hip dysplasia, but to date few studies have demonstrated which parameters are of most importance for predicting surgical outcomes.

PURPOSE

To identify preoperative radiographic parameters that are associated with poor outcomes in the arthroscopic treatment of adult mild hip dysplasia.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

Radiographic analysis was performed in patients with mild hip dysplasia who underwent arthroscopic surgery between 2009 and 2015. Preoperative radiographic measurements included lateral center edge angle, Tönnis angle, neck shaft angle, anterior center edge angle, alpha angle, femoral head extrusion index, and acetabular depth-to-width ratio. Failure was defined as failure to achieve the minimal clinically important difference (MCID) utilizing the modified Harris Hip Score or as the need for secondary operation. The equal variance t test was used to analyze radiographic parameters. Statistical significance was determined using a P value of .05.

RESULTS

A total of 373 hips underwent analysis with an average follow-up of 41 months (range, 24-102 months). Of these, 46 hips (12%) required secondary operation, and 95 (25%) failed to meet the MCID. The overall failure rate was 32.4%. There was no single measurement or combination thereof associated with failure to reach the MCID. Higher preoperative Tönnis angles were associated with secondary operation, with a mean of 6.7° (95% CI, 5.3°-8.1°) in the secondary operation group versus 4.8° (95% CI, 4.4°-5.3°) in the nonsecondary operation group (P = .006). The odds ratio was 1.12 (95% CI, 1.0-1.2; P = .05) per degree increase in Tönnis angle for secondary operation. In patients with a Tönnis angle >10°, 84% required secondary operation.

CONCLUSION

Higher Tönnis angles portend a higher risk for revision surgery. The probability of secondary operation was increased by a magnitude of 1.12 with each degree increase in the Tönnis angle. In patients with a Tönnis angle >10°, 84% required a secondary operation.

Superiority of the modified Tönnis angle over the Tönnis angle in the radiographic diagnosis of acetabular dysplasia

The aim of this study was to evaluate the limitations of the Tönnis angle as one of the most commonly used parameters in the diagnosis of acetabular dysplasia, and to explore the feasibility of the modified Tönnis angle in the diagnosis of acetabular dysplasia. A total of 224 patients (120 females and 104 males) with 448 hips, aged between 15 and 83 years (median, 45.0 years), were selected for the measurement of the center-edge (CE) and Tönnis angles. To evaluate the relative position of the medial edge of the acetabular sourcil, a new parameter, known as the center-medial-edge (CME) angle, was designed. As an improvement of the Tönnis angle, a new angle preliminarily termed the modified Tönnis angle was created. In addition, the degree of clarity of the medial edge of the acetabular sourcil on radiograph was evaluated, and the hips were divided into the clear-edge and blurred-edge groups. The hips belonging to the blurred-edge group could not be used for Tönnis angle measurements. All measurements were performed digitally using the tool of the picture-archiving communication system. Among the 448 acetabular sourcils, 142 had a blurred medial edge (31.7%). The mean value of the CME angle was 37.94°, with a range of 21.76–63.99°. The 95% prediction interval of the modified Tönnis angle was estimated to be −6.39 to 11.73°. The correlation coefficients were −0.838 between the CE and Tönnis angles, 0.889 between the Tönnis and modified Tönnis angles and −0.905 between the CE and modified Tönnis angles. In conclusion, the modified Tönnis angle can substitute for the Tönnis angle without joint space narrowing and subluxation of the hip, particularly when the Tönnis angle cannot be measured due to a blurred medial edge of the acetabular sourcil on pelvic radiograph.