Radiographic geometric measures of the hip joint and abductor muscle function in patients after total hip replacement

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.

What happens to the gluteus medius in young and middle-aged patients with hip dysplasia?

BACKGROUND

Much research has focused on quantifying the bony characteristics of patients with developmental dysplasia of the hip (DDH). Far less attention, however, has been paid to muscle abnormalities around the hip such as those in the gluteus medius (GM).

METHODS

We retrospectively examined clinical and imaging data, such as the age of onset and computed tomography (CT) findings, in 108 consecutive hips. Subjects for the control group were selected from our radiology database. Two readers independently evaluated the length (LGM), cross-sectional area (CSA), width (WGM), and thickness (TGM) of the GM and arm of GM (AGM) and angle of the GM activation (AOA) and bony parameters including the acetabulum-head index (AHI), lateral central edge angle (LCEA), acetabular index (AI), femoral offset (FO), and height of the rotation centre of femoral head (HCFH) among all cases using the imaging data.

RESULTS

The patient group included 108 hips. The AGM, LGM, CSA, and TGM were lower in the DDH patients, while AOA was higher. However, there was no significant difference in the WGM between the two groups. Multiple linear regression analysis showed that AGM and AOA were independent factors affecting LCEA. The following regression equation was used: Y(LCEA) = 5.377 * X1 (AGM) - 0.310 * X2 (AOA) - 11.331. The mechanical characteristics of the GM and many bony parameters were significantly correlated (the AGM and AHI, LCEA, AI, FO, but not HCFH; AOA and AHI, LCEA, AI, but not FO or HCFH). The CSA was positively correlated with only HCFH. The rest were not statistical significance linear correlation. The multivariate regression results showed that the age of onset was positively correlated with AGM (r = 0.467). The regression equation used was Y = 9.0 * X (age of onset) - 11.4.

CONCLUSION

We found difference in the morphological and mechanical characteristics of the GM between hips with DDH and hips of normal morphology. Of note, the mechanical characteristics of the GM were influenced by bony parameters in patients with DDH.

The accuracy of digital templating in cementless total hip arthroplasty in dysplastic hips

Background

Total hip arthroplasty (THA) for developmental dysplasia of the hip (DDH) is a complex procedure due to associated anatomical abnormalities. We studied the extent to which preoperative digital templating is reliable when performing cementless THA in patients with DDH.

Methods

We templated and compared the pre- and postoperative sizes of the acetabular and femoral components and the center of rotation (COR), and analysed the postoperative cup coverage, leg length discrepancy (LLD), and stem alignment in 50 patients (56 hips) with DDH treated with THA.

Results

The implant size exactly matched the template size in 42.9% of cases for the acetabular component and in 38.2% of cases for the femoral component, whereas the templated ±1 size was used in 80.4 and 81.8% of cases for the acetabular and femoral components, respectively. There were no statistically significant differences between templated and used component sizes among different DDH severity levels (acetabular cup: p = 0.30 under the Crowe classification and p = 0.94 under the Hartofilakidis classification; femoral stem: p = 0.98 and p = 0.74, respectively). There were no statistically significant differences between the planned and postoperative COR (p = 0.14 horizontally and p = 0.52 vertically). The median postoperative LLD was 7 (range 0–37) mm.

Conclusion

Digital preoperative templating is reliable in the planning of cementless THA in patients with DDH.

Effect of preoperative limb-length discrepancy on abductor strength after total hip arthroplasty in patients with developmental dysplasia of the hip

BACKGROUND

Limb-length discrepancy (LLD) arising from hip subluxation or dislocation and accompanied by insufficiency of hip abductor in patients with developmental dysplasia of the hip (DDH) can be corrected partially or completely with total hip arthroplasty (THA). However, information about post-THA changes in abductor strength related to preoperative LLD in patients with DDH is lacking. We aimed to explore the post-THA recovery course of abductor muscle strength and its related factors in patients with DDH.

METHODS

A cohort of 45 patients with unilateral DDH was divided into two groups according to their Crowe classification: patients with class I or II DDH formed Group M, and patients in class III and IV DDH formed Group S. The following parameters were measured on standardized antero-posterior hip radiographs taken in the supine position pre- and post-THA: abductor muscle length, abductor lever arm, LLD, and femoral offset (FO). Abductor strength was evaluated quantitatively with the Isomed 2000 isokinetic test system (1 week before the operation and 1, 3, 6, and 12 months after the operation). The contralateral normal hip joint served as a within-patient control. The affected side:healthy side ratios of the parameters above were calculated.

RESULTS

Abductor strength ratio evaluated at the five follow-up time points was larger in Group M than that in Group S (p < 0.001). The average abductor strength ratio reached 78.5, 85.4, and 89.2% at the 3, 6, and 12 months postoperative exams, respectively, in Group M, and reached 50.3, 63.2, and 72.9% in Group S. The abductor muscle length ratio, the abductor muscle level arm ratio, and the FO ratio were significantly increased postoperatively, relative to preoperative assessment, in the two groups. LLD was reduced significantly postoperatively, relative to preoperative values, in both groups. Both preoperative LLD (r = -0.791, p < 0.001) and the change in abductor muscle length ratio (r = -0.659, p < 0.001) correlated with abductor strength recovery.

CONCLUSION

Patients showed the greatest improvement in abductor strength within the first 6 months after THA, especially during the first 3 months. Abductor strength was consistently greater in patients with mild dysplasia than in patients with severe dysplasia. The extent of preoperative LLD and the increase in abductor length were related with post-THA abductor strength recovery in patients with DDH.

Changes of gluteus medius muscle in the adult patients with unilateral developmental dysplasia of the hip

Background

The gluteus medius muscle is essential for gait and hip stability. Changes that occur in the gluteus medius muscles in patients with developmental dysplasia of the hip (DDH) are not well understood. A better understanding of DDH related changes will have positive repercussions toward hip soft tissue reconstruction.

Methods

19 adult patients with unilateral DDH scheduled for total hip arthroplasty were assessed for: cross-sectional area (CSA), radiological density (RD) and the length of gluteus medius using computed tomograhpy(CT) (scanned before THA). Hip abductor moment arm and gluteus medius activation angle were also measured via hip anteroposterior radiographs.

Results

Both CSA and RD of gluteus medius muscle were significantly reduced (p < 0.05) in the affected hip compared to the control. In the affected hip, the length of the gluteus medius muscle was reduced by 8-11 % (p < 0.05) while the gluteus medius activation angle was significantly increased (p < 0.05) and the hip abductor moment arm was decreased (p < 0.05).

Conclusions

The gluteus medius showed substantial loss of CSA, RD as well as decreased length in patients with DDH in the affected hip. These changes should be considered in both hip reconstruction and postoperative rehabilitation training in patients with DDH.