Hip physical examination extension loss and radiographic osseous findings in patients with low back pain and nonarthritic hips

Abstract

The association between hip and spine abnormalities is frequent, and limitation in hip extension has been linked with low back pain. The purpose of this study was to assess the radiographic osseous findings in nonarthritic hips of patients with hip pain, low back pain, and limited hip extension. Ninety patients (92 hips) were included in this study. Hip extension was tested in the contralateral decubitus position with the hip in neutral abduction/adduction and neutral rotation. In sequence, hip extension was tested by adding passive abduction, followed by internal/external rotation of the hip. A hip extension limitation was defined as less than zero degrees of extension. Imaging studies were assessed for the following osseous morphologies: decreased ischiofemoral space (≤17 mm), increased femoral torsion (≥30°), decreased femoral torsion (≤5°), and posterior acetabular overcoverage. Fifty-seven out of 92 hips (62%) had at least one osseous imaging finding for limitation in hip extension: decreased ischiofemoral space (38/92, 41%), increased femoral torsion (5/92, 5%), decreased femoral torsion (24/92, 26%), and posterior acetabular overcoverage (21/92, 23%). Decreased ischiofemoral space, femoral torsional abnormalities, and/or posterior acetabular wall overcoverage are observed in imaging studies of most individuals with limitation of hip extension and low back pain.

Pathologies limiting hip flexion, especially femoroacetabular impingement, have been frequent subjects of orthopedic hip research over the last three decades.¹ However, pathologies limiting hip extension (HE) are more important for activities that require an upright posture.^2,3 While a loss of HE in nonarthritic hips is traditionally linked to tightness of the musculotendinous structures anterior to the hip joint,^4–6 osseous etiologies such as ischiofemoral impingement and abnormal femoral torsion can also limit HE.^7–11 The association between hip and spine abnormalities is known as hip-spine syndrome, and limitation in HE has been associated with low back pain (LBP).^8,12 Given the potential link between osseus abnormalities and limited HE, the purpose of this study was to assess radiographic osseous findings in nonarthritic hips of patients with hip pain, LBP, and limited HE. A secondary purpose was to determine the utility of adding abduction and internal and external rotation to HE during the physical examination to assess the osseous contribution to limited HE.

METHODS

This study was carried out in an urban academic tertiary-care orthopedic facility and was approved by the hospital’s institutional review board. A retrospective review was performed in 341 patients who had an initial office visit for hip pain between October 2018 and September 2019. Inclusion criteria were presence of LBP (reported by patients as a symptom during their initial visit), limited HE on physical examination, and absence of hip osteoarthritis. Exclusion criteria were absence of LBP, normal HE, coxofemoral osteoarthritis (Tönnis 2 or 3),³ total hip arthroplasty, and incomplete imaging studies. In total, 90 patients (92 hips) with a mean (± standard deviation [SD]) age of 46.1 ± 15 years were included. This group comprised 71 (79%) women and 19 (21%) men. Radiographs and magnetic resonance imaging (MRI) were assessed for the following osseous findings of limitation in HE: decreased ischiofemoral space (≤17 mm), increased femoral torsion (≥30°), decreased femoral torsion (≤5°), and posterior acetabular overcoverage (posterior acetabular wall crossing at least 2 mm lateral to the center of the femoral head in anteroposterior pelvis radiographs).¹³

HE was assessed at first office visits by a fellowship-trained hip surgeon (HDM) before the MRI was performed. The patient was positioned in the contralateral decubitus position and the examined hip was brought in neutral abduction/adduction and neutral internal/external rotation into terminal HE (Figure 1). The HE was considered limited if a blockage with a firm endpoint was noticed and impeded extension past zero degrees in neutral abduction/adduction and neutral rotation, resulting in pelvic and lumbar compensatory motion in the sagittal plane. In sequence, HE was tested by adding passive internal rotation, external rotation, and abduction of the hip. Improvements in HE, along with reduced back pain and spinal motion, were noted for each of the three positions (Figure 2, Supplementary material, Video 1).

Figure 1.

Hip extension testing. (a) Start position with the hip in neutral rotation and neutral abduction. (b) Limited hip extension with compensatory lumbopelvic movement (blue line) and recreation of low back pain (red arrow).

Figure 2.

Effects of internal rotation, external rotation, and abduction during hip extension. (a) Internal rotation, with pain relief and reduced spinopelvic motion observed in patients with increased femoral torsion. (b) External rotation, improving hip extension in decreased femoral torsion. (c) Abduction, improving extension in patients with ischiofemoral impingement (impingement between the lesser trochanter and ischium).

An orthopedic surgeon (MH) screened the radiographic images and performed the imaging measurements. Complete radiographic studies consisted of the anteroposterior standing pelvis, lateral hip, and Lequesne’s false profile of the affected hip.¹⁴ An anteroposterior radiograph of the pelvis was utilized to identify posterior acetabular overcoverage. The following radiographic parameters were also assessed: femoral neck-shaft angle, acetabular center edge angle, acetabular inclination, lateralization of the femoral head, and joint space.^13,15,16 The acetabular parameters were assessed in studies demonstrating symmetric obturator foramens, with a distance of 1 to 3 cm from the pubic symphysis to the tip of the coccyx (Merge Pacs, Watson Health Imaging, Chicago, IL). The false profile of Lequesne view was utilized to measure the anterior center-edge angle.

All MRI studies were performed with the patient in a supine position. Two patients had neurostimulators implanted in their low back, and the assessments were performed utilizing computed tomography. Acetabular version and femoral torsion were assessed on axial images obtained with the patient supine and the feet taped midfoot stance position.¹⁷ The acetabular version was measured in the axial cut at the greatest distance between the anterior and posterior acetabular walls.¹⁸ Femoral torsion measurements were assessed using the posterior surface of the femoral condyles at the knee as the distal reference and the femoral neck axis in the first axial cut distal to the femoral head as the proximal reference¹⁹ (Figure 3). The McKibbin index was determined by adding the acetabular version to the femoral torsion.¹⁸ Ischiofemoral distance and quadratus femoris space were measured according to Torriani et al²⁰ (Figure 4).

Figure 3.

Determination of the femoral torsion. Right femoral neck oriented posteriorly (–10°) associated with 23° of internal rotation at the knee, resulting in a femoral torsion of 13°.

Figure 4.

Axial MRI of the right hip demonstrating the ischiofemoral space (blue line) and quadratus femoris space (red line). The ischiofemoral space represents the smallest distance between the lateral cortex of the ischial tuberosity and medial cortex of the lesser trochanter. The quadratus femoris space is the smallest space for passage of the quadratus femoris muscle between the superolateral surface of the hamstring tendons and the posteromedial surface of the iliopsoas tendon or lesser trochanter.

Independent sample t tests were utilized to assess differences in ischiofemoral distance between hips with increased HE in abduction and hips with no increased HE in abduction (alpha = 0.05) and to compare the femoral torsion between hips with increased HE in internal/external rotation and hips without increased HE in internal/external rotation (alpha = 0.05). The radiographic and MRI assessments were evaluated for intra- and interrater reliability in 20 random hips from the 92 included hips. These measurements were compared to those taken by a senior orthopedic surgery resident (SN) to determine the interrater reliability. Precision of measurement by a single observer and between observers was determined by calculating the 95% confidence interval between the repeated measurements and their average using MedCalc v19.2.1software (Table 1).

Table 1.

Intra- and interrater reliability of the imaging parameters

Parameter	Intrarater ICC	Interrater ICC
Acetabular version	0.953	0.934
Femoral torsion	0.977	0.92
McKibbin index	0.971	0.928
Ischiofemoral space	0.966	0.946
Quadratus femoris space	0.936	0.922
Posterior overcoverage	0.773	0.773

ICC indicates intraclass correlation coefficient (Cohen’s kappa coefficient).

RESULTS

Patient demographics, along with clinical and imaging assessments, are presented in Table 2. Of the 92 hips, 57 (62%) had imaging studies with at least one osseous finding of limitation in HE. The most common osseous finding of limited HE was decreased ischiofemoral space (38/92, 41%), followed by decreased femoral torsion (24/92, 26%), posterior acetabular overcoverage (21/92, 23%), and increased femoral torsion (5/92, 5%) (Table 3). One osseous finding limiting HE was identified in 29 of 92 hips (32%), two osseous findings in 25 hips (27%), and three osseous findings in 3 hips (3%). No obvious osseous finding for limited HE was observed in 35 (38%) of the 92 hips.

Table 2.

Demographic and imaging characteristics of 92 hips (90 patients) with hip pain, low back pain, and limitation in hip extension

Variable	Female	Male	Total
Number of hips	73	19	92
Age (years)	44.6 ± 14.9	51.8 ± 14.7	46.1 ± 15
Body mass index (kg/m2)	24.7 ± 5.4	27 ± 2.9	25.2 ± 5.1
Duration of symptoms (years)	2.7 ± 2.9	4.4 ± 7.2	3 ± 4
Hip internal rotation	25° ± 16.8°	17.4° ± 7.9°	23.5° ± 15.7°
Hip external rotation	39.3° ± 21.8°	40.8° ± 19.8°	39.6° ± 21.3°
Neck shaft angle	134.5° ± 4.2°	134.2° ± 4.1°	134.5° ± 4.1°
Acetabular inclination	5.2° ± 5°	5.1° ± 3.2°	5.2° ± 4.7°
Center edge angle	34.5° ± 6.3°	35.8° ± 4.1°	34.8° ± 5.9°
Anterior center edge angle	33.9° ± 6.5°	35.5° ± 4.8°	34.2° ± °6.2
Ischiofemoral space (mm)	18.8 ± 8.4	21.9 ± 5.3	19.4 ± 7.9
Quadratus femoris space (mm)	12.5 ± 6.3	16 ± 4	13.2 ± 6
Femoral torsion	12.5° ± 10.7°	11.1° ± 12.7°	12.2° ± 11.1°
Acetabular version	20.3° ± 6.6°	16.7° ± 4°	19.5° ± 6.3°
McKibbin index	32.8° ± 14.1°	27.8° ± 14.7°	31.8° ± 14.3°

Table 3.

Prevalence of osseous findings of limitation in hip extension in 92 hips (90 patients) with hip pain and low back pain

Osseous finding	Number of hips	Percentage of total (92 hips)
Decreased ischiofemoral space (≤17 mm)	38	41%
Decreased femoral torsion (≤5°)	24	26%
Increased femoral torsion (≥30°)	5	5%
Posterior acetabular overcoverage	21	23%

On physical examination, addition of abduction allowed further HE without pelvic and lumbar compensation in 28 hips, which were found to have, on average, decreased ischiofemoral space (16.9 ± 6.8 mm). In comparison, 64 hips in which abduction did not increase HE presented a mean ischiofemoral space of 20.5 ± 8.2 mm (P = 0.04). Addition of external rotation allowed further HE without pelvic and lumbar compensation in 24 hips, which were found to have, on average, decreased femoral torsion (6.8° ± 10.4°). In comparison, 68 hips in which external rotation did not increase HE without pelvic and lumbar compensation presented, on average, femoral torsion of 14.5° ± 10.6° (P = 0.002). Addition of internal rotation allowed further HE in 17 hips, which presented, on average, femoral torsion of 17.6° ± 11.7°. In comparison, 75 hips in which internal rotation did not increase HE presented, on average, femoral torsion of 11° ± 10.6° (P = 0.02).

DISCUSSION

This study demonstrated that 57 (62%) of the 92 hips with HE limitation presented at least one osseous finding of decreased ischiofemoral space, abnormal femoral torsion, or posterior acetabular overcoverage that could lead to hip pain and LBP. Hips with decreased ischiofemoral space, decreased femoral torsion, and increased femoral torsion demonstrated increasing terminal HE with the addition of abduction, external rotation, and internal rotation, respectively. The present investigation supports testing terminal HE by sequentially adding hip abduction, internal rotation, and external rotation to estimate the osseous contribution to limited HE in nonarthritic hips.

In a cadaveric study by Morris et al, increased femoral torsion and acetabular version resulted in premature contact between the femoral neck and acetabulum.¹⁰ However, increased acetabular version does not imply posterior acetabular overcoverage, especially in hips with a lateralized femoral head. Therefore, the relationship between the posterior acetabular wall and center of the femoral head was utilized in the present study as a more logical contributor than acetabular version to limited HE. A limitation in the aforementioned cadaveric study was the inclusion of specimens without ligamentous or musculotendinous structures.¹⁰ The absence of an obvious osseous etiology in 35 (38%) hips with HE in our study indicates the fundamental role of musculotendinous and ligamentous structures in limiting HE. Tightness of the musculotendinous structures such as the iliopsoas, sartorius, rectus femoris, or tensor fascia lata muscle should be considered in patients with limited HE.^4–6 The rectus femoris, sartorius, and tensor fascia lata muscles cross both the hip and knee joint, and the degree of knee flexion should be controlled during hip physical examination and assessment of HE. Increased terminal HE by extending the knee may indicate a contribution of one of the aforementioned musculotendinous structures in limiting HE. Long-lasting limited HE due to osseus etiologies may also lead to the subsequent tightening of anterior ligamentous and musculotendinous structures.

In patients with femoral torsion abnormalities, the ligamentous structures play a role in limiting HE. Patients with increased femoral torsion and laxity of the iliofemoral ligament may be able to further extend the hip due to anterior subluxation of the femoral head with a posterior levering mechanism. In contrast, HE limitation would be observed in hips with increased femoral torsion and a tight iliofemoral ligament. The effects of this mechanism were observed in the present study. Hips with increased femoral torsion were able to further extend with the addition of internal rotation, which simultaneously relaxes the iliofemoral ligament and avoids premature coupling between the posterior femoral neck and acetabulum. For hips with decreased femoral torsion, the migration of the iliofemoral ligament medial arm superolaterally to the femoral head likely explains why additional HE is achieved with external rotation. This effect depends on the degree of hip abduction, the femoral neck shaft angle, and the relationship between the origin and insertion of the iliofemoral ligament medial arm in the coronal plane. Hips with decreased femoral torsion may not present limitation in extension due to lax pubofemoral, iliofemoral, and ischiofemoral ligaments. Therefore, femoral torsion and ligamentous structures have a close relationship in controlling HE. Of note, a cam deformity was not considered an obvious osseus finding of limited HE in the present study. However, a superiorly located cam deformity has the potential to tighten the iliofemoral and ischiofemoral ligaments, limiting HE.

This study presents a number of limitations. First, the ligamentous and musculotendinous structures may contribute to limitation in HE in patients with osseous abnormalities. Second, HE limitation was not quantitatively defined (i.e., the degrees of maximal HE). Third, related to the lack of quantitative definition for HE limitation, test-retest reliability analysis for the HE maneuvers on physical examination was not performed.

Decreased ischiofemoral space, femoral torsional abnormalities, or posterior acetabular wall overcoverage are observed in imaging studies of most individuals with limitation of HE. Testing HE in abduction and internal and external rotation is helpful to diagnose osseus causes of limited HE.