Patient Inclusion and Data Collection
After obtaining institutional review board approval, we used our longitudinally maintained institutional database to evaluate all patients treated with hip arthroscopy for labral tears between January 2009 and December 2011. The study group included all patients with adequate followup who underwent hip arthroscopy for labral treatment and then required conversion surgery to THA. The control group included all patients with adequate followup who underwent hip arthroscopy for labral treatment but who did not have conversion surgery to THA. Inclusion criteria were all patients undergoing primary or revision hip arthroscopy for a symptomatic labral tear. Exclusion criteria were patients with previous hip conditions such as Legg-Calvé-Perthes disease, slipped capital femoral epiphysis, pigmented villonodular synovitis, ankylosing spondylitis, and avascular necrosis. The database includes demographics, clinical history, patient-reported outcomes scores, and radiographic data.
We collected 41 preoperative and intraoperative variables on patients during the study period. These variables were based on the following characteristics: (1) demographics; (2) scoring instruments used; (3) radiographic factors; and (4) intraoperative findings.
These individual variables based on the four characteristics included: age, sex, BMI, workers compensation status, revision surgery status, history of back pain, previous back surgery, months of symptoms, modified Harris hip score, nonarthritic hip score, hip outcome score-activities of daily living, hip outcome score-sport-specific subscale, VAS, femoral anteversion, Tönnis grade, lateral center-edge angle (LCEA), anterior center-edge angle (ACEA), acetabular inclination, alpha angle, joint space measurements, and crossover sign percentage. Intraoperative variables included: Seldes labral tear grade, labral tear size, acetabular labrum articular disruption (ALAD) grade, acetabular chondral defect size, acetabular Outerbridge grade, femoral chondral defect size, femoral Outerbridge grade, ligamentum teres tear grade, labral treatment (repair versus débridement), traction time, number of labral anchors, capsular treatment (release versus repair), acetabuloplasty, femoral osteoplasty, iliopsoas release, notchplasty, microfracture, and loose body removal. The type and grade of chondral lesion for the acetabulum and femoral head were recorded using the Outerbridge classification. Peripheral acetabular labral-articular disruption lesions were classified according to the ALAD classification: softening of cartilage adjacent to the labrum (ALAD1), early peel back of the cartilage (ALAD2), large chondral flap (ALAD3), or complete loss of cartilage (ALAD4).
Demographics and Followup
Of the 893 patients who underwent hip arthroscopy and who met study inclusion criteria, 792 (89%) were available for followup. Seventy-two patients (9%) who underwent conversion surgery to THA during the followup period constituted the study group, and 720 patients (91%) who did not undergo conversion surgery to THA during the followup period constituted the control group. One hundred one patients were lost to followup. Mean time to conversion to THA for the study group was 19 ± 12 months (range, 0.9–52 months), and the average time to followup for the control group was 31 ± 8.months (range, 20–62 months). The entire patient population had an average age of 38 ± 14 years (range, 13–76 years) and an average BMI of 25 ± 4.8 kg/m2 (range, 16–48 kg/m2). There were 293 (37%) men and 499 (63%) women. Four hundred twenty-four (54%) underwent right hip surgery, and 368 (46%) underwent left hip surgery. The proportion of right and left hip procedures was not different between groups. Seventy-eight (9.8%) procedures involved a workers’ compensation claim, and 81 (10%) procedures were revision hip arthroscopy.
At our institution preoperative and postoperative radiographic data on all patients undergoing hip arthroscopy are recorded by hip preservation fellows once the patient reaches the 2-year followup. The measurements were taken by multiple readers, however previous interobserver reliability has been shown from our group , but was not tested for the current study. Using the supine AP pelvis radiograph, the LCEA, acetabular inclination, acetabular crossover, and Tönnis grade were measured . When a crossover sign was present we estimated the percent of crossover by dividing distance from the superior acetabulum to the point of intersection of the anterior and posterior wall by the entire length of the posterior wall. This was done to gauge the amount of acetabular retroversion. A 45°-Dunn view was used to measure the alpha angle. A false profile view was used to measure the ACEA. The joint space is measured in three places on an AP pelvic radiograph: the medial and the lateral edges of the sourcil and the central aspect of the sourcil. Femoral anteversion was collected from preoperative MR images when performed at our center.
Indications for Hip Arthroscopy
Clinically all patients had signs and symptoms of a labral tear and did not respond to 3 months of nonoperative treatment. Patients had groin pain, or pain surrounding their hip, with positive impingement maneuvers for a minimum of 3 months. Nonoperative treatment included a minimum of 6 weeks of physical therapy and a trial of antiinflammatory medication. During the preoperative workup patients underwent plain radiographs as detailed above. Patients also underwent MRI or an MRI arthrogram to confirm labral disorders.
All surgeries were performed by the senior author (BGD), with the patient in the modified supine position, using a minimum of two portals. After establishment of portals and capsulotomy, a diagnostic arthroscopy of the hip was performed to evaluate for loose bodies, chondral defects, labral tears, ligamentum teres tears, and other intraarticular disorders. An intraoperative data sheet was collected on all patients at the time of diagnostic arthroscopy. Labra were repaired when possible. If labral tissue quality was unable to be repaired, patients were treated with débridement or reconstruction. The acetabular rim was resected when features of pincer impingement were present. After addressing lesions in the central compartment, the peripheral compartment was exposed and femoral osteoplasty performed for cam lesions. Surgical treatments were recorded in our database.
Intraoperative Data Recording
At our institution a detailed intraoperative data sheet is recorded for all patients undergoing hip arthroscopy. At the time of surgery labral tear size was documented for all patients using traditional acetabular clock-face nomenclature to determine size and location of the tear. Labral tears were described using the classification of Seldes et al. , with Type I tears being separation at the chondrolabral junction and Type II tears being intrasubstance damage. To describe the position of the labral tear, the acetabulum is divided into 12 sectors corresponding to a clock face. Labral tear size was documented by recording the number of sectors involved in the tear. An arthroscopic probe is used to measure chondral damage on the femoral head and acetabulum in square centimeters.
The postoperative rehabilitation was patient-specific depending on concomitant procedures. In general, patients were advised to use partial, 20-pound weightbearing for 2 to 6 weeks.
Patients wore a hip abduction brace for 2 weeks postoperatively. Hip ROM was limited to 90° flexion, neutral internal rotation, 30° external rotation, and 30° abduction for 3 to 6 weeks. When the patient was full weightbearing, therapy was advanced to achieve full strength and activity by 3 to 4 months.
Up to 41 potential predictors were assessed simultaneously using a multivariate (multivariable), backward, stepwise Cox proportional hazard model regression using the 41 potential candidate predictors. A liberal probability less than 0.10 variable retention criterion was used. This probability was used, rather than 0.05, to ensure potentially important variables were not eliminated. The rate ratio (RR) for the simultaneously significant variables is reported along with the corresponding 95% confidence bounds and p values. For a continuous variable such as age, the RR is for a one-unit increase in the variable. For example, if the RR for age is 1.06, this is 1.06 per year. That is, for a 1-year increase in age, the event rate is 6% larger. For a K-unit increase the, RR is RRK. So, for a K = 5-year increase in age, the RR in this example is 1.065 × 5 = 1.34, implying that a 5-year age increase is associated with a 34% increase in the total hip replacement rate.
The accuracy of the Cox model was assessed using the Harrell C statistic . The linear relation between the log hazard versus continuous variables such as age was confirmed by fitting cubic splines. For example, to see that there was a linear relation between the log hazard and age, age and the cubic spline of age were fit. If the relationship is linear, only age, not the spline of age, should be statistically significant.
To use all 792 cases in the multivariate Cox model, missing values were first imputed using Markov chain Monte Carlo methods . Results were similar to those using only complete cases.
Using the results of the multivariate regression, we developed a simplified calculator that may be helpful in counseling a patient regarding the risk of conversion surgery to THA after hip arthroscopy. Variables chosen were based on the results of the multivariate analysis. Points for certain values of variables were assigned based on hazard ratios. We then weighted the variable to develop a 100-point scale. These points can be added and the sum used to predict the risk of conversion to THA at 27 months followup based on the hazard ratios.