Increased Inferior Capsular Thickness on Magnetic Resonance Imaging Is Associated With Adhesive Capsulitis of the Hip

Purpose

To investigate magnetic resonance imaging (MRI) findings associated with adhesive capsulitis of the hip and identify differences in capsular thickness between patients with the diagnosis and controls matched by age, sex, and body mass index (BMI).

Methods

Consecutive patients with the diagnosis of adhesive capsulitis of the hip were identified and included for retrospective chart review and compared with an equal number of age, sex, and BMI-matched controls. Patients were excluded if they had prior hip surgery or did not have an MRI or magnetic resonance arthrography (MRA) obtained at our institution to allow for calibrated measurement. Quantitative data were collected on capsular thickness in 4 locations (anterior, posterior, superior, inferior) and MRA filling ratios. Nonquantitative data were collected regarding the presence or absence of labral tears.

Results

Fourteen patients were included along with 14 controls. Patients with adhesive capsulitis have significantly thicker inferior capsules compared with controls (3.43 vs 2.50 mm; P =.014). Anterior (3.93 vs 3.86 mm; P =.923), posterior (3.57 vs 3.14 mm; P =.362), and superior (5.29 vs 3.57 mm; P =.156) capsular thickness, as well as filling ratios, did not differ in a statistically significant manner. Categorical evaluation of labral tearing did not demonstrate statistically significant differences.

Conclusions

Adhesive capsulitis of the hip is associated with thicker inferior joint capsules compared to age, sex, and BMI-matched controls. No differences were found in the thickness of anterior, posterior, or superior joint capsules.

Level of Evidence

Level III, retrospective diagnostic case-control.

Adhesive capsulitis of the hip represents a potentially underappreciated diagnosis characterized by nonspecific chief complaints. ^,^,^,^,^, Most commonly, patients present with globally decreased hip range of motion—especially in rotation—in the absence of arthritis, and pain exacerbated by activity or weight-bearing. ^,^,^,^,^, Similar to adhesive capsulitis of the shoulder, adhesive capsulitis of the hip is largely considered a diagnosis of exclusion. ^,^,^,

Recent work has sought to investigate treatment options and outcomes for this diagnosis, but it remains evident that the diagnostic process itself remains a challenge for musculoskeletal physicians. ^,^,^,^,^,^, Challenges in making the diagnosis of adhesive capsulitis of the hip are the result of several factors, including the fact that decreased hip range of motion may be due to hip conditions other than adhesive capsulitis, advanced imaging findings can be difficult to interpret, and there are no standardized diagnostic criteria for adhesive capsulitis. This difficulty in diagnosis can likely, in part, be attributed to the fact that the existing literature on adhesive capsulitis of the hip is largely limited to case reports and relatively small series of patients. ^,^, However, as awareness of this entity has increased, so too has the drive to investigate techniques and tools to successfully diagnose and treat it.

Recent studies have explored the ability to identify features on magnetic resonance imaging (MRI), magnetic resonance arthrography (MRA), and computed tomography arthrography (CTA) that are associated with adhesive capsulitis of the hip. ^,^,^,^, Some of these imaging findings have shown promise, with data suggesting possible differences in joint cavity filling ratios and specific areas of capsular thickness. ^,^, The purpose of this present study was to investigate MRI findings associated with adhesive capsulitis of the hip and identify differences in capsular thickness between patients with the diagnosis and controls matched by age, sex, and body mass index (BMI). The hypothesis was that capsular thickness would be increased in patients diagnosed with adhesive capsulitis compared to controls, as seen in prior limited case reports and small case series, as well as in adhesive capsulitis of the shoulder.

Methods

Information on consecutive patients diagnosed by the senior author (M.R.S.) with adhesive capsulitis from 2010 to 2020 was retrospectively collected. The senior author has a busy sports medicine practice with an emphasis on nonarthritic hip pathology. Clinical diagnosis of adhesive capsulitis was made by the senior author and was based on the patient’s chief complaint of limited hip range of motion and/or hip pain, accompanied by a physical exam finding of globally decreased hip range of motion and, particularly, loss of external rotation. Additionally, all patients had an absence of evidence of impingement, degenerative disease, or an alternative diagnostic explanation for restricted range of motion based on radiographic imaging and MRI/MRA. One control patient from the senior author’s clinic schedule without the diagnosis of adhesive capsulitis was retrospectively selected for each case patient by manually matching for age, sex, and BMI to control for this potential confounder in capsular thickness.

Inclusion criteria for the present study were (1) patients aged 18 or older, (2) diagnosis of adhesive capsulitis of the hip, as described above, and (3) absence of other identifiable hip pathology that would explain the global restricted range of motion seen on physical exam. Patients were excluded who (1) had prior hip surgery; (2) had an MRI or MRA obtained outside our health care system and, thus, were unable to be calibrated for measurement; (3) had joint space narrowing, subchondral cysts, or osteophytes on x-ray; and (4) had a history of inflammatory arthropathy. Age, sex, and BMI-matched controls were selected after identification of cases.

Radiography and MRI were independently evaluated for quantitative and categorical variables by 1 fellowship-trained musculoskeletal radiologist (J.Y.) and 1 orthopaedic surgeon (D.V.C.), and quantitative measurements were averaged. Data collected from radiography included lateral center edge angle. Quantitative data collected on MRI/MRA (10 MRIs per group, 4 MRAs per group) included anterior capsule thickness, posterior capsule thickness, superior (lateral) capsule thickness, inferior (medial) capsule thickness, as well as both anterior-to-posterior (AP) and superior-to-inferior (SI) filling ratios for patients with MRA studies. Filling ratios reflect joint distensibility. The AP filling ratio was calculated as the widest distance of the anterior joint cavity to the widest distance of the posterior joint cavity, and the SI filling ratio was calculated as the widest distance of the superior joint cavity to the widest distance of the inferior joint cavity. For consistency, anterior and posterior capsular measurements were made on axial images at the level of the center of the femoral physeal scar, and superior and inferior measurements were made using the same landmarks on the coronal images ( Fig 1 ). Categorical data collected from MRI/MRA included the presence of labral tearing and ligamentum teres tears. Quantitative variables between cases and controls were compared using Mann–Whitney U tests given the sample size of the study was small, and the data was not normally distributed. Categorical variables were compared using Fisher’s exact test. P value threshold of.05 was used for statistical significance.

Image, AltText currently not available — Fig. 1

The center of the femoral head physeal scar was identified in coronal ( Fig 1 A), sagittal ( Fig 1 B), and axial ( Fig 1 C) planes simultaneously using a linked MRI viewer. Anterior and posterior capsular thickness measurements were made on the corresponding axial images. Superior and inferior measurements were made on the corresponding coronal images

Results

Seventeen patients with mean age 48 years (range: 32–61, SD 9.0) with adhesive capsulitis of the hip were identified for imaging evaluation. Three cases were excluded from MRI/MRA evaluation due to noncalibrated studies, leaving 14 cases to compare to 14 age, sex, and BMI-matched controls. Two patients in both the case group and the control group had a history of diabetes. Two patients in the control group had a history of hypothyroidism. Average age of both groups was 48 years (cases range from 32 to 61, SD 9.7; controls range from 32 to 65, SD 9.1). Thirteen of the 14 (93%) patients in each group were female. Average BMI was 28 among cases (SD 5.6) and 29 among controls (SD 5.0). Among the cases, 12 presented with a chief complaint of hip pain and 2 patients presented with limited range of motion; however, all patients with adhesive capsulitis had a global reduction in hip range of motion on actual physical exam. Among the controls, iliopsoas tendinitis was the most common diagnosis, presenting in 7 (50%) of patients. Diagnoses of the control group are shown in Table 1 . No statistically significant differences were identified on radiographic evaluation. Lateral center edge angle was 30.4° (SD = 5.76) for the study group and 33.4° (SD = 4.69) for controls ( P =.16), with an interobserver variability intraclass correlation coefficient for radiographic measurements of 0.81.

Table 1

Control Group Diagnoses

Diagnosis	Number of Patients (%)
Iliopsoas tendinitis	7 (50)
Femoroacetabular impingement	2 (14.3)
Piriformis syndrome	1 (7.1)
Labral tear (non-FAI)	1 (7.1)
External snapping hip	1 (7.1)
Ligamentum teres tear	2 (14.3)
Trochanteric bursitis	2 (14.3)
Meralgia paresthetica	1 (7.1)