Restricted passive hip range of motion (ROM) is an essential component of clinical diagnosis for various hip pathologies, including femoroacetabular impingement (FAI), osteoarthritis (OA), and femoral or acetabular version abnormalities.1–4 Preoperative measurements of hip ROM also provide a baseline for evaluating the efficacy of surgical interventions aimed at correcting underlying structural deformities.5,6
Despite this, the diagnostic reliability of passive hip ROM measurement remains controversial. Intra- and interobserver reliability has ranged from poor to excellent for clinical measurements of hip ROM performed in young asymptomatic adults,7,8 patients with early-onset coxarthrosis,9–11 and patients undergoing hip arthroscopy.12,13 This variation has largely been attributed to operator error, including items such as measurement error,9 improper hip positioning,14 and poorly sensitive measurement protocols.10,15–17 However, few studies have examined the potential effects of patient-specific characteristics such as pain threshold, apprehension, or inhibition on measurements of passive hip ROM.
As part of the standard of care in the current authors' hip preservation service, measurement of passive hip ROM is first obtained in the clinic and subsequently repeated under general anesthesia preceding hip arthroscopy. The purpose of this study was to compare measurements of hip ROM performed in clinic and under general anesthesia in patients suffering from various painful hip pathologies. The hypothesis was that passive hip ROM would be increased across all measures of hip ROM under anesthesia vs without due to anesthetic-mediated elimination of voluntary neurosensory characteristics.
Materials and Methods
After institutional review board approval was obtained, the authors performed a single-center prospective study on a consecutive cohort of 260 patients undergoing hip arthroscopy. Inclusion criteria for patients selected for this study were as follows: (1) persistent hip pain and mechanical symptoms refractory to nonoperative management lasting at least 3 months, (2) reproducible clinical examination findings suggestive of impingement or instability, and (3) joint space width more than 3 mm on all views of plain radiography and 3-dimensional (3-D) computed tomography (CT).18 Common indications for hip arthroscopy included in this study were symptomatic FAI, hip instability due to dysplasia (prior to periacetabular osteotomy), and/or excessive femoral torsion (prior to femoral derotational osteotomy). Patients undergoing additional surgical treatment for diagnoses of slipped capital femoral epiphysis (SCFE), Legg-Calvé-Perthes disease, osteochondromatosis, or post-dislocation syndrome were excluded.
The following demographic data were recorded for all patients: age, diagnosis, side of surgery, sex, height, weight, and self-reported levels of weekly physical activity.
As part of a comprehensive clinical examination of the spine, hip, and pelvis,19 passive ROM was evaluated bilaterally with the patient placed in supine, prone, and lateral positions, respectively. All measurements of passive hip ROM with and without anesthesia were evaluated through visual estimation by an experienced orthopedic surgeon (O.M.-D.) to minimize interobserver variability. Measurements of passive hip flexion, internal rotation (IR), and external rotation (ER) ROM at 90° flexion were conducted following stabilization of the pelvis in the supine position. Hip abduction ROM was measured with the patient placed in the supine position and the hip in neutral position (0° flexion/extension). Hip extension ROM was measured with the patient positioned in lateral decubitus, and external and internal rotation ROM of the hip in neutral position were measured with the patient prone and the knees at 90° of flexion. A bilateral hip quadrant (FADIR [flexion, adduction, and internal rotation]) test was then performed with the patient positioned supine and the hip flexed, adducted, and internally rotated. Immediately prior to the arthroscopic procedure, a bilateral clinical examination of the hip joint was performed following induction of general anesthesia with the patient placed in the supine position.
The degree of agreement between visual estimation and digital goniometry was evaluated in a blinded random subset of 100 hips using a 2-way, mixed, absolute-agreement single-measures intra-class correlation coefficient (ICC). Values greater than 0.80 indicated excellent reliability; 0.61 to 0.80 indicated substantial reliability; 0.41 to 0.60 indicated moderate reliability; 0.21 to 0.40 indicated fair reliability; and less than 0.20 indicated poor reliability.20 Accordingly, the ICC demonstrated excellent reliability for measurements of passive hip ROM by visual estimation (ICC=0.976; 95% confidence interval, 0.727–0.992).
Patients underwent a standardized series of plain radiographs, including anteroposterior (AP) pelvic and cross-table lateral views, and preoperative CT scans with 3-D surface-rendered reconstruction of the whole pelvis. Joint space width was assessed as the narrowest space between the bony contour of the acetabular rim and femoral head using the digital caliper Office PACS system (Stryker, Flower Mound, Texas) on all AP radiographs. Lateral center-edge angle (LCEA), cranial and equatorial acetabular version, and femoral version and torsion were measured on CT scans with 1-mm slice thickness and 2-mm reconstruction in the axial, sagittal, coronal orthogonal, and oblique axial (oriented parallel to the long axis of femoral neck) planes.21 Reformatted coronal slices were reconstructed around the realigned vertical axis passing through the femoral head center from posterior to anterior positions. Additional axial CT images were obtained through the knee joint with a field of view from 2 cm above the patellar apex to 2 cm below the fibular head.
Clinical diagnoses of bony impingement and acetabular dysplasia were confirmed according to accepted pathomorphologic signs and measurements.21,22 Suggestive physical examination findings included reductions in hip flexion and internal rotation ROM and positive findings of impingement on provocative testing (eg, FABER [flexion, abduction, and external rotation], FADIR).23 Confirmative imaging findings included acetabular retroversion (crossover sign or ischial spine sign), LCEA exceeding 40°, and/or acetabular inclination less than 0° for pincer FAI; alpha angle exceeding 50° on radial sequences of the head-neck junction and femoral head-neck offset ratio less than 0.18 for cam FAI; and LCEA less than 20° for acetabular dysplasia.
Descriptive statistics were reported as means and SDs for quantitative variables and as counts and frequencies for categorical variables. All variables were evaluated for distribution of normality using a combination of histograms, Q-Q plots, and the Shapiro-Wilk test (normality indicated by P>.05). The significance of mean differences between hip ROM measurements performed with and without anesthesia were evaluated using the paired-samples t test (parametric) or Wilcoxon signed rank test (nonparametric). Statistical significance for all comparisons was set at a P value less than .05 (2-tailed). All analyses were conducted using SPSS version 22.0 statistical software package (IBM, Armonk, New York).
Participants and Descriptive Data
The study cohort comprised 260 patients (78 males and 182 females) with a mean age of 33.7±11.1 years and mean body mass index (BMI) of 24.0±4.6 kg/ m2. Among the 520 hips included in this study, 152 (29.2%) showed features of symptomatic mixed FAI, 73 (14.0%) of cam FAI, 60 (11.5%) of pincer FAI, 17 (3.3%) of hip dysplasia, and 16 (3.1%) of FAI with concomitant hip dysplasia. A total of 150 contralateral hips in patients undergoing unilateral surgery had no discernible pathology (per clinical and radiographic evaluation) and were therefore included as a healthy control group. Additional baseline characteristics are summarized in Table 1.
Patient Demographics and Baseline Characteristics (N=260)
Effect of Anesthesia on Measurement of Passive Hip Range of Motion
Overall, induction of general anesthesia resulted in a statistically significant reduction in hip abduction ROM (43° vs 42°; mean difference, −1°; P=.006) and hip flexion ROM (112° vs 110°; mean difference, −2°; P=.006) (Table 2). In contrast, measurement of hip external rotation ROM at 90° of hip flexion was increased by a mean of 2° following induction of anesthesia (47° vs 49°; P=.008). Measurements of hip internal rotation ROM at 90° of hip flexion did not vary significantly between conditional states with and without anesthesia (17.0° vs 16.5°; mean difference, −0.5°; P=.688).
Measurement of Hip ROM in the Clinic Versus Under General Anesthesia According to Etiology
Subgroup Analysis According to Clinical Diagnosis
In healthy contralateral hips of patients presenting with unilateral hip pathology, a mean reduction of 4° in hip flexion ROM (115° vs 111°; P<.001) and 2° in hip abduction ROM (44° vs 42°; P=.01) was observed following induction of anesthesia. In contrast, hip external rotation ROM at 90° of hip flexion was increased by 4° in hips with pincer FAI pathology (48° vs 52°; P=.02) and 6° in dysplastic hips (47° vs 53°; P=.02), respectively, following induction of anesthesia. For all other components of passive hip ROM, there was no statistically significant difference between measurements performed with and without anesthesia among control, FAI, hip dysplasia, or FAI with concomitant hip dysplasia cohorts (P>.05 in all cases).
This prospective study shows that measurements of hip external rotation ROM at 90° of hip flexion are statistically significantly increased with induction of general anesthesia in patients with pincer FAI or hip dysplasia. However, these changes are likely not clinically significant. Limitations in hip external rotation ROM at 90° of hip flexion are predominantly thought to occur secondary to extra-articular mechanical conflict between the greater trochanter and pubic ramus.24 In patients with pincer FAI, bony outgrowth at the lateral aspect of the acetabular rim impedes external rotation of the femoral head within the acetabular socket. In contrast, patients with hip dysplasia tend to experience restricted hip ROM due to pain and apprehension arising as a consequence of labral tear, iliopsoas pathology, and significant joint inflammation.25 Induction of anesthesia may result in significant relaxation of the anterior capsule and musculature, thereby enabling an increase in external rotation. On the contrary, no significant difference was found between measurements of hip internal rotation at 90° of flexion. This is likely a result of bony landmarks inhibiting further ROM under anesthesia.
Measurements of passive hip flexion ROM and hip abduction ROM were predominantly decreased following induction of anesthesia in the healthy contralateral hip of patients presenting with unilateral hip pathology. Although statistically significant, the differences in these ROM measurements were small (hip flexion, 4°; hip abduction, 2°) and are therefore probably clinically insignificant. It is possible that during clinical examination without anesthesia, patients with healthy hips may have accommodated the examiner's flexion maneuver by tilting their pelvis, whereas this would not occur under anesthesia. However, this is just an assumption and would have to be proven with further studies.
A paucity of research investigating hip ROM with and without anesthesia renders a comparative analysis of this study's results difficult. Fujishiro et al26 reported a universal increase of 5° to 10° across all measurements of passive hip ROM evaluated under general anesthesia in a cohort of 444 patients undergoing primary total hip arthroplasty (THA). By comparison, observed differences in the current study were more localized and were often of lesser magnitude. The authors attribute these smaller differences to the diminished severity of symptoms and extent of hip deformity in their patient cohort relative to patients indicated for THA.
Strengths of this study include its prospective study design, large sample size, and inclusion of a wide variety of hip pathologies. However, the authors acknowledge the following limitations. First, the presented cohort represents a single surgeon's experience at a dedicated hip preservation practice and may not be applicable to all clinical settings. In addition, all measurements of passive hip ROM were evaluated by visual estimation only. Although standardized testing methods have been reported to improve accuracy of measurement,27 the authors' past experience demonstrated an excellent rate of concordance between visual estimation and digital goniometry. Finally, several differences between measurements of hip ROM with and without anesthesia, although statistically significant, were relatively minor. Additional studies are required to inform clinical usefulness in these cases.
Regardless of a patient's hip pathology, there is no clinically significant difference in any preoperative hip ROM measurements following induction of general anesthesia.
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Patient Demographics and Baseline Characteristics (N=260)
|Age, mean±SD, y||32.7±11.1|
|Male, No.||78 (30.0%)|
|Height, mean±SD, cm||169.8±10.1|
|Weight, mean±SD, kg||70.4±16.5|
|BMI, mean±SD, kg/m2||24.2±4.6|
|Clinical diagnosis, No.|
| No pathology||150 (28.9%)|
| Mixed FAI||152 (29.2%)|
| Cam FAI||73 (14.0%)|
| Pincer FAI||60 (11.5%)|
| Hip dysplasia||17 (3.3%)|
| FAI and hip dysplasia||16 (3.1%)|
| Other||52 (10.0%)|
Measurementa of Hip ROM in the Clinic Versus Under General Anesthesia According to Etiology
|No pathology (control)||48.7±9.7||49.8±10.8||1.1±0.8||.057||19.1±12.9||16.9±13.6||−2.2±0.9||.010d||43.5±6.8||41.7±6.2||−1.8±0.7||.010d||115.3±13.2||111.1±10.8||−4.2±1.0||<.001d|
|FAI and hip dysplasia||49.3±8.3||48.2±11.0||−1.1±0.4||.774||16.3±10.1||21.4±12.6||5.1±3.2||.072||43.3±4.5||42.2±4.8||−1.1±1.1||.227||113.8±11.5||108.4±10.8||−5.4±0.6||.195|