Can the change in center-edge angle during pincer trimming be reliably predicted?

How Reliable Is the Measurement of the Lateral Center Edge Angle on Scoliosis Radiographs for Detecting Acetabular Dysplasia?

PURPOSE

Hip dysplasia reportedly occurs in up to 12% of the general population and may be higher in patients with adolescent idiopathic scoliosis (AIS). When using lateral center edge angle (LCEA) measurements to help identify hip dysplasia, it is uncertain if this measurement can be performed reliably on scoliosis radiographs due to parallax. The purpose of this study is to evaluate the reliability of measuring LCEA on scoliosis radiographs compared with standard pelvis radiographs.

METHODS

This study evaluated 40 hips on 20 patients (mean age 12.5 years ± 3.1; 50% Female) who received PA scoliosis radiographs and AP pelvis radiographs within 1 year of each other. Review was performed by 4 pediatric radiologists (2 general, 2 MSK), 2 pediatric orthopaedic surgeons, and 1 research fellow. Radiographic measurement of the LCEA for each hip was first performed on the scoliosis radiograph. After a minimum of 3 days, the LCEA was measured on a pelvis radiograph of the same individual obtained within 1 year of the scoliosis radiograph. Pearson coefficient was used to measure agreement between scoliosis and pelvis radiograph measurements. Intraclass correlation coefficient (ICC) was used to evaluate intraobserver and interobserver agreement. ICC values <0.5 were classified as poor reliability, 0.5 to 0.75 were classified moderate, 0.75 to 0.90 were classified good, and >0.9 indicated excellent reliability.

RESULTS

The mean difference between scoliosis and pelvis radiographs was 54 ± 79 days. There was good-to-excellent interobserver agreement on LCEA measurements made between readers on scoliosis radiographs (ICC: 0.94, 95% CI: 0.90-0.96, P <0.001) and pelvis radiographs (ICC: 0.91, 95% CI: 0.83-0.95, P <0.001), and moderate-to-excellent intraobserver agreement for scoliosis radiographs (ICC range: 0.68 to 0.98; P <0.001) and pelvis radiographs (ICC range: 0.62 to 0.96; P <0.001). There was a strong correlation between LCEA measurements made on scoliosis and pelvis radiographs ( r2 =0.66, P <0.001), and the intermodality agreement between scoliosis and pelvis radiograph LCEA measurements were moderate to good (ICC range: 0.68 to 0.89, P <0.001).

CONCLUSIONS

Overall, there was good-to-excellent agreement between readers on scoliosis and pelvis radiographs, respectively, and moderate-to-excellent intraobserver agreement between LCEA measurements made on scoliosis radiographs and pelvis radiographs, respectively. LCEA measurements made on scoliosis radiographs strongly correlated to the measurements made on pelvis radiographs, and the intermodality ICC was also considered moderate to good. Dedicated pelvis radiographs may not be necessary during scoliosis workup and follow-up surveillance, thereby decreasing radiation exposure, cost, and improving patient care workflow.

LEVEL OF EVIDENCE

Level IV-diagnostic study.

Relationship between the Depth of Acetabuloplasty and Outcomes of Hip Arthroscopy in Patients with Global Pincer Femoroacetabular Impingement: Study with a Minimum Follow-Up Period of 2 Years

OBJECTIVE

There has been no definite consensus on the ideal depth of acetabuloplasty, especially in cases of global pincer femoroacetabular impingement (FAI). This study aims to determine whether the depth of acetabuloplasty influences postoperative outcomes in cases of global pincer FAI.

METHODS

Data were retrospectively collected from patients with global pincer FAI who underwent hip arthroscopy with a minimum follow-up period of 2 years from May 2014 to December 2018. Patients with global pincer FAI were subdivided into low or high resection depth groups based on whether the intraoperative acetabular rim was resected by more than 3 mm. Radiographic measurements; arthroscopic procedures; preoperative and postoperative PROs were recorded. Achievement of MCID and PASS was compared for the VAS, mHHS, HOS-ADL, and iHOT-12. A paired Student t-test was used to evaluate the significance of preoperative and postoperative PROs and two-tailed unpaired Student t-test was used to compare demographic data and PROs between different groups. MCID and PASS were evaluated using the chi-square test or the Fisher's exact test.

RESULTS

A total of 41 hips with global pincer FAI (15 and 26 patients in low or high resection depth groups, respectively) were included in this study. Both groups showed significant postoperative improvements in the scores of all PROs (p < 0.001). Compared to the low resection depth group, the high resection depth group had a lower degree of improvement through hip arthroscopy, which manifested as lower postoperative mHHS scores (94.29 vs. 85.08, p = 0.006), higher VAS scores (0.93 vs. 2.54, p = 0.002), and lower improvements in VAS (-5.00 vs. -3.35, p = 0.028), HOS-ADL (34.99 vs. 23.90, p = 0.017) and iHOT-12 (39.89 vs. 29.27, p = 0.036). Patients in high resection depth group were less likely to achieve the MCID for the VAS score compared to low resection depth group in significant (73.3 vs. 26.9%, p = 0.004).

CONCLUSIONS

For patients with global pincer, the outcomes in high resection depth group were slightly worse than the the low resection depth group. It is indicated that excessive resection of the acetabular rim during the procedure should be avoided.

Propensity-Matched Patients Undergoing Revision Hip Arthroscopy Older Than the Age of 40 Years Had Greater Risk of Conversion to Total Hip Arthroplasty Compared With Their Primary Counterparts

PURPOSE

To report patient-reported outcomes (PROs) and survivorship following revision hip arthroscopy in patients aged ≥40 years and to compare these results with a propensity-matched primary hip arthroscopy control group.

METHODS

Data were prospectively collected and retrospectively reviewed for all patients who underwent revision hip arthroscopy between June 2008 and January 2019. Patients were included if they were ≥40 years of age at the time of surgery and had minimum 2-year follow-up for the modified Harris Hip Score, Nonarthritic Hip Score, Visual Analog Scale for pain, and the Hip Outcome Score-Sports Specific Subscale. Patients who had a previous hip condition, or those who lacked minimum 2-year follow-up, were excluded. The revision group was further analyzed by conducting a 1:1 propensity-matched sub-analysis to a primary hip arthroscopy control group based on age, sex, body mass index, and acetabular labrum articular disruption grade. Statistical significance was set at P < .05.

RESULTS

Eighty-nine hips (92.7% follow-up) were included, with 66.3% being females. The mean age, body mass index, and follow-up time were 49.4 ± 8.0 years, 26.6 ± 4.1, and 62.7 ± 38.5 months, respectively. Significant improvement in all PROs (P < .001) was reported, and 71.8%, 58 74.4%, and 65.2% achieved the minimal clinically important difference for the modified Harris Hip Score, Nonarthritic Hip Score, and Hip Outcome Score-Sports Specific Subscale, respectively. Eighty-seven revision hips were successfully propensity-matched to 87 primary hips. Both groups reported similar improvement for all PROs, but the relative risk of conversion to total hip arthroplasty was 2.63 times greater (95% confidence interval 1.20-5.79) for the revision group.

CONCLUSIONS

Patients aged ≥40 years who underwent revision hip arthroscopy reported significant improvement in all PROs at a mean follow-up of 62.7 months with favorable rates of achieving the minimal clinically important difference. When compared to the propensity-matched control group, both achieved similar rates of improvement, but the revision group was 2.63 times more likely to convert to total hip arthroplasty.

LEVEL OF EVIDENCE

III. case-control study.

Hip Arthroscopic Surgery in the Context of Femoroacetabular Impingement Syndrome, Labral Tear, and Acetabular Overcoverage: Minimum 5-Year Outcomes With a Subanalysis Against Patients Without Overcoverage

BACKGROUND

Improvement in patient-reported outcomes (PROs) has been reported in the short term after hip arthroscopy for femoroacetabular impingement syndrome (FAIS) and labral tear in the setting of acetabular overcoverage. Yet, there is a paucity of information in the literature on midterm PROs.

PURPOSE

To (1) report minimum 5-year PROs in patients who underwent primary hip arthroscopy for FAIS and acetabular labral tears in the context of acetabular overcoverage and (2) compare outcomes with those of a propensity-matched control group without acetabular overcoverage.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Data were prospectively collected and retrospectively analyzed on all patients who underwent hip arthroscopy for FAIS and labral tears between February 2008 and November 2013. Inclusion criteria were lateral center-edge angle >40° and minimum 5-year follow-up for the modified Harris Hip Score (mHHS), Nonarthritic Hip Score (NAHS), and the Hip Outcome Score-Sports-Specific Subscale (HOS-SSS). Exclusion criteria were previous ipsilateral hip surgery or conditions, active workers' compensation claims, or lack of minimum 5-year outcomes. A 1:1 propensity-matched comparison was made between the study group and a control group without acetabular overcoverage (lateral center-edge angle, 25°-40°) based on age at surgery, sex, body mass index, Tönnis grade, laterality, and follow-up time. The minimal clinically important difference (MCID) was calculated for the mHHS, HOS-SSS, and NAHS. Secondary surgical procedures were recorded.

RESULTS

A total of 54 patients satisfied the inclusion criteria for the study group, of whom 45 (83.3%; 45 hips) had a minimum 5-year follow-up and were matched without differences in age at surgery, sex, body mass index, or follow-up time. The study and control groups demonstrated significant and comparable improvements for the mHHS (mean ± SD Δ, 24.06 ± 24.19 vs 26.33 ± 17.27; P = .625), NAHS (Δ, 31.22 ± 25.31 vs 27.15 ± 17.61; P = .399), and HOS-SSS (Δ, 33.16 ± 34.73 vs 34.75 ± 26.15; P = .557). The rates for achieving the MCID were similar for the study and control groups for the mHHS (76.7% vs 84.2%; P = .399), HOS-SSS (79.1% vs 75.8%; P = .731), and NAHS (81.4% vs 84.2%; P = .738). Need for revision surgery was similar (P = .748). A lower conversion rate to total hip arthroplasty was reported for the study than for the control group (2.2% vs 15.6%; P = .026).

CONCLUSION

In the context of FAIS, labral tears, and acetabular overcoverage, patients who underwent hip arthroscopy reported significant improvement in several PROs at minimum 5-year follow-up. Moreover, outcomes were comparable with those of a propensity-matched control group without acetabular overcoverage. Furthermore, the rate of achieving the MCID for the mHHS, HOS-SSS, and NAHS was similar between these groups.

Hips With Acetabular Retroversion Can Be Safely Treated With Advanced Arthroscopic Techniques Without Anteverting Periacetabular Osteotomy: Midterm Outcomes With Propensity-Matched Control Group

BACKGROUND

Different options, from reverse (anteverting) periacetabular osteotomy to hip arthroscopy, have been proposed for surgical treatment of femoroacetabular impingement syndrome (FAIS) in the setting of acetabular retroversion.

PURPOSE

(1) To report and analyze midterm patient-reported outcome scores (PROs) in patients with FAIS and labral tears in the setting of acetabular retroversion after isolated hip arthroscopy and (2) to compare these PROs with those of a propensity-matched control group without acetabular retroversion.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Prospectively collected data were retrospectively reviewed for patients who underwent hip arthroscopy for FAIS and labral tear treatment between June 2008 and March 2014. Inclusion criteria were as follows: acetabular retroversion, pre- and postoperative PROs for modified Harris Hip Score (mHHS), Non-arthritic Hip Score, Hip Outcome Score-Sports Specific Scale (HOS-SSS), and visual analog scale (VAS). Propensity score matching was utilized to identify a control group without acetabular retroversion matched 1:1 with similar age, sex, body mass index, acetabular and femoral head Outerbridge grade, preoperative lateral center-edge angle, and labral treatment. Patient acceptable symptomatic state (PASS) and/or minimal clinically important difference (MCID) for the mHHS, HOS-SSS, International Hip Outcome Tool-12, and VAS was calculated.

RESULTS

A total of 205 hips with acetabular retroversion were matched to a control group. The groups showed no difference in demographic variables. The retroversion group was composed of 139 female and 66 male hips, with a mean ± SD age of 23.81 ± 7.28 years and follow-up time of 65.24 ± 20.31 months. Intraoperative diagnostic data and procedures performed were similar between groups, except more femoroplasties were performed in the retroversion group. Significant improvements for the mHHS, Non-arthritic Hip Score, HOS-SSS, and VAS were seen for both groups at a mean 5-year follow-up. The proportion of patients who reached the PASS and MCID were similar.

CONCLUSION

In the setting of FAIS and labral tears, patients with acetabular retroversion can be safely treated with advanced hip arthroscopic techniques without reverse (anteverting) periacetabular osteotomy in a high-volume surgeon's hands. Patients with acetabular retroversion demonstrated favorable PROs at midterm follow-up. Furthermore, the proportion of patients reaching the MCID and PASS for several PROs were comparable with those of a propensity-matched control group without acetabular retroversion.

Mirror Image Modeling of Acetabular Rim Thickness Differences in Patients With Unilateral Femoroacetabular Impingement Syndrome

Purpose

To use mirror imaging to identify the location and magnitude of difference in acetabular rim morphology between the symptomatic and unaffected acetabula in patients with symptomatic unilateral pincer-type or mixed femoroacetabular impingement syndrome (FAIS) using 1-dimensional models created with computed tomography (CT).

Methods

CT scans of bilateral hips in 33 patients diagnosed with unilateral pincer-type or mixed FAIS were obtained. Three-dimensional bilateral hip models were constructed, and the unaffected hemipelvis was superimposed onto the symptomatic side to compare acetabular thickness. Protrusion of the symptomatic side was recorded, and rim morphology was divided into clock face quadrants to analyze the location of greatest magnitude of difference between affected and unaffected acetabula. Analysis of the quadrants was performed using analysis of variance with post hoc Bonferroni correction.

Results

The study group consisted of more females (51.6%) than males, with an average age of 35.72 ± 7.8 years and an average body mass index of 24.3 ± 4.1 kg/m². Of the 33 hips included, 14 were isolated pincer-type FAIS and 19 were mixed. The average preoperative symptomatic side lateral center edge angle was 37.5° ± 7.2° compared with 29° ± 5.1° on the asymptomatic side (P = .001). The symptomatic acetabular rim was on average 0.43 ± 0.18 mm thicker than the corresponding location on the unaffected rim. When the acetabulum was divided into clock face quadrants, the 12 to 3 o'clock position showed the greatest difference between symptomatic and unaffected sides (0.55 ± 0.18 mm) compared with the 3 to 6 o'clock position (0.4 ± 0.28 mm; P = .006), 6 to 9 o'clock (0.34 ± 0.07 mm; P < .001), and 9 to 12 o'clock (0.38 ± 0.03; P = .001).

Conclusions

Patients with unilateral, symptomatic pincer-type or mixed FAIS show statistical differences in rim thickness between the affected and unaffected acetabula. Small changes in acetabular rim morphology on the order of ≤0.5 mm may be the difference between symptomatic FAIS and the unaffected hip.

Level of Evidence

IV, case series.

Radiographic and Clinical Outcomes of Adolescents With Acetabular Retroversion Treated Arthroscopically

BACKGROUND

Retroversion of the acetabulum is a cause of pincer impingement. Symptomatic retroversion has traditionally been treated with anteverting periacetabular osteotomy (PAO). However, arthroscopic rim trimming can also treat pincer impingement associated with acetabular retroversion. The purpose of this study was to report the outcomes and radiographic findings in a series of adolescent patients with symptomatic acetabular retroversion treated arthroscopically.

METHODS

Data were prospectively gathered at a single institution using an established hip preservation registry. Patients below 18 years with a retroverted acetabulum that underwent primary hip arthroscopy with 2-year follow-up were included. Acetabular retroversion was defined by 3 radiographic criteria: the presence of crossover, ischial spine sign, and posterior wall sign. Radiographic measurements of the lateral center-edge angle, anterior center-edge angle, alpha angle, and crossover percentage were reported preoperatively and postoperatively. Patient-reported outcome (PROs) measures included the modified Harris Hip Score, the non-Arthritic Hip Score, Hip Outcome Score Sports Subscale, visual analog scale, and patient satisfaction, recorded at 3 months, 1 year, and 2 years, postoperatively. In addition, International Hip Outcome Tool scores were gathered at 2 years.

RESULTS

Between April 2008 and July 2014, there were 43 patients (48 hips) treated with hip arthroscopy who met the inclusion criteria. The average age was 16.1 years (range, 13.9 to 17.9 y) and there were 38 females and 10 males. The average follow-up was 50.4 months, with a minimum of 2 years. Statistically significant improvements in all PROs were found at 2 years postoperatively. There were 9 hips with lateral center-edge angle ≤25 degrees; the PROs of this group was not different than patients with normal coverage. Three patients underwent arthroscopic revision. No patient subsequently underwent anteverting PAO during the study period. There were no reported complications.

CONCLUSIONS

Femoroacetabular impingement caused by acetabular retroversion treated with hip arthroscopy demonstrates good outcomes at 2 years with a low complication rate. Symptomatic adolescents may be safely and successfully treated arthroscopically, potentially avoiding anteverting PAO.

STUDY DESIGN

Level of evidence 4-case series.

Is Increased Acetabular Cartilage or Fossa Size Associated With Pincer Femoroacetabular Impingement?

BACKGROUND

Surgical treatment for pincer femoroacetabular impingement (FAI) of the hip remains controversial, between trimming the prominent acetabular rim and reverse periacetabular osteotomy (PAO) that reorients the acetabulum. However, rim trimming may decrease articular surface size to a critical threshold where increased joint contact forces lead to joint degeneration. Therefore, knowledge of how much acetabular articular cartilage is available for resection is important when evaluating between the two surgical options. In addition, it remains unclear whether the acetabulum rim in pincer FAI is a prominent rim because of increased cartilage size or increased fossa size.

QUESTIONS/PURPOSES

We used reformatted MR and CT data to establish linear length dimensions of the lunate cartilage and cotyloid fossa in normal, dysplastic, and deep acetabula.

METHODS

We reviewed the last 200 hips undergoing PAO, reverse PAO, and surgical dislocation for acetabular rim trimming at one institution. We compared MR images of symptomatic hips with acetabular dysplasia (20 hips), pincer FAI (29 hips), and CT scans of asymptomatic hips from patients who underwent CT scans for reasons other than hip pain (20 hips). These hips were chosen sequentially from the underlying pool of 200 potential subjects to identify the first 10 male and the first 10 female hips in each group that met inclusion criteria. As a result of low numbers, we included all hips that had undergone reverse PAO and met inclusion criteria. Cartilage width was measured medially from the cotyloid fossa to the lateral labrochondral junction. Cotyloid fossa linear height was measured from superior to inferior and cotyloid fossa width was measured from anterior to posterior. Superior lunate cartilage width (SLCW) and cotyloid fossa height (CFH) were measured on MR and CT oblique coronal reformats; anterior lunate cartilage width (ALCW), posterior lunate cartilage width (PLCW), and cotyloid fossa width (CFW) were measured on MR and CT oblique axial reformats. Cohorts were compared using multivariate analysis of variance with Bonferroni's adjustment for multiple comparisons.

RESULTS

Compared with control acetabula, dysplastic acetabula had smaller SLCW (2.08 ± 0.29 mm versus 2.63 ± 0.42 mm, mean difference = -0.55 mm; 95% confidence interval [CI] = -0.83 to -0.27; p < 0.01), ALCW (1.20 ± 0.34 mm versus 1.64 ± 0.21 mm, mean difference = -0.44 mm; 95% CI = -0.70 to -0.18; p = 0.00), CFH (2.84 ± 0.37 mm versus 3.42 ± 0.57 mm, mean difference = -0.59 mm; 95% CI = -0.96 to -0.21; p < 0.01), and CFW (1.98 ± 0.50 mm versus 2.77 ± 0.33 mm, mean difference = -0.80 mm; 95% CI = -1.16 to -0.42; p < 0.0001). Based on the results, we identified two subtypes of deep acetabula. Compared with controls, deep subtype 1 had normal CFH and CFW but increased ALCW (2.09 ± 0.42 mm versus 1.64 ± 0.21 mm; p < 0.001) and PLCW (2.32 ± 0.36 mm versus 2.00 ± 0.32 mm; p = 0.04). Compared with controls, deep subtype 2 had increased CFH (4.37 ± 0.51 mm versus 3.42 ± 0.57 mm; p < 0.01) and CFW (2.76 ± 0.54 mm versus 2.77 ± 0.33 mm; p = 1.0) but smaller SCLW (2.12 ± 0.40 mm versus 2.63 ± 0.42 mm; p < 0.01).

CONCLUSIONS

Deep acetabula have two distinct morphologies: subtype 1 with increased anterior and posterior cartilage lengths and subtype 2 with a larger fossa in height and width and smaller superior cartilage length.

CLINICAL RELEVANCE

In patients with deep subtype 1 hips that have increased anterior and posterior cartilage widths, rim trimming to create an articular surface of normal size may be reasonable. However, for patients with deep subtype 2 hips that have large fossas but do not have increased cartilage widths, we propose that a reverse PAO that reorients yet preserves the size of the articular surface may be more promising. However, these theories will need to be validated in well-controlled clinical studies.

Clinical Outcomes of Hip Arthroscopy in Radiographically Diagnosed Retroverted Acetabula

BACKGROUND

Symptomatic global retroversion of the acetabulum, as diagnosed on plain radiographs of the pelvis, has traditionally been treated with reverse periacetabular osteotomy, which improves posterior undercoverage and eliminates the anterior pincer lesion. There is a paucity of literature on hip arthroscopy in this group, secondary to theoretical concern of iatrogenic dysplasia, subsequent instability, and arthritis.

PURPOSE

To evaluate the outcomes of hip arthroscopy for patients with a radiographic diagnosis of acetabular retroversion, using patient-reported outcomes, visual analog scale (VAS), patient satisfaction, and pre- and postoperative Tönnis grades.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Pre- and postoperative data were prospectively collected and retrospectively reviewed for patients who underwent hip arthroscopy at 1 institution between June 2008 and February 2012. Data were analyzed for patients who had adequate radiographs of the pelvis that demonstrated global acetabular retroversion and who were treated with arthroscopic surgery. Complications were tracked in this institution's database. The modified Harris Hip Score, Nonarthritic Hip Score, Hip Outcome Score (HOS)-activities of daily living subscale, and HOS-sport-specific subscale, and VAS were analyzed preoperatively and at latest follow-up. Level of postoperative satisfaction was assessed on a scale of 0 to 10. Pre- and postoperative alpha angle, lateral center-edge angle, anterior center-edge angle, crossover percentage, and Tönnis grade were recorded. Tönnis grade at latest follow-up was utilized to determine progression of osteoarthritis.

RESULTS

A total of 82 hips among 78 patients were identified who met the listed criteria. The mean age of the patients was 23 years, and the mean follow-up was 39 months. These patients showed statistically significant improvement in modified Harris Hip Score (preoperative to ≥2-year follow-up: 65 to 81), Nonarthritic Hip Score (65 to 86), HOS-activities of daily living subscale (69 to 88), HOS-sport-specific subscale (47 to 76), and VAS (5.9 to 2.5) (P < .0001). In terms of satisfaction with the surgery, they had an mean score of 7.4. There were 3 minor complications, none of which required reoperation. One patient underwent hip arthroplasty at 6 months after hip arthroscopy. Fifteen patients had >2-year radiographic follow-up; none of these patients had an increase in Tönnis grade as compared with the preoperative state.

CONCLUSION

This study demonstrates that hip arthroscopy can successfully treat femoroacetabular impingement associated with a globally retroverted acetabulum at a minimum 2-year follow-up. Survivorship was 99% at 2 years, with 1 patient requiring further surgery in the form of hip arthroplasty. There was no noted progression of Tönnis grade at final follow-up. The procedure was extremely safe, with a minor complication rate of 3.6%.

Imaging in Hip Arthroscopy for Femoroacetabular Impingement: A Comprehensive Approach

Hip arthroscopy has experienced unprecedented growth in recent years and remains an area of booming technology and interest in orthopedic surgery. As understanding of the pathologic state of femoroacetabular impingement (FAI) has grown, imaging modalities have increased. Careful consideration of all bony and soft tissue structures in concert with physical examination findings in nonarthritic patients is necessary before any surgical intervention. This article summarizes the authors' approach to imaging in patients suspected of FAI, which facilitates careful patient selection and preoperative planning.

Effects of acetabular rim trimming on hip joint contact pressures: how much is too much?

BACKGROUND

In patients with femoroacetabular impingement (FAI), acetabular rim trimming removes the offending area of the acetabular deformity in patients with pincer-type and mixed-type FAI to improve hip joint kinematics. Although the rationale for arthroscopic acetabular rim trimming in patients with FAI is well established, the amount of rim resection has not been quantified, and the threshold at which excessive rim resection results in abnormal hip contact pressures has not been described.

PURPOSE

To investigate the changes in contact areas, contact pressures, and peak forces within the hip joint with sequential acetabular rim trimming.

STUDY DESIGN

Controlled laboratory study.

METHODS

Six fresh-frozen, nondysplastic, human cadaveric hemipelvises were analyzed utilizing thin-film piezoresistive load sensors to measure the contact area, contact pressure, and peak force after anterosuperior acetabular rim trimming at depths of 0 mm (intact), 2 mm, 4 mm, 6 mm, and 8 mm. Each specimen was examined at 20° of extension and 60° of flexion. Analysis was performed on 2 regions of interest: the acetabular rim and the acetabular base (deep part of the acetabulum). After each experimental condition, the acetabulum was normalized with respect to the intact state to account for specimen variability. Statistical analysis was conducted through 1-way analysis of variance with post hoc Games-Howell tests.

RESULTS

At the acetabular base, there were significant increases in the contact area after 4-mm resection (60°: 169.12% ± 30.64%; P = .0138), contact pressure after 6-mm resection (60°: 292.76% ± 79.07%; P = .009), and peak force after 6-mm resection (60°: 166.00% ± 34.40%; P = .027). At the acetabular rim, there were significant decreases in the contact area after 6-mm resection (60°: 66.32% ± 18.80%; P = .0354) (20°: 65.47% ± 15.87%; P = .0127), contact pressure after 6-mm resection (60°: 50.77% ± 11.49%; P < .001) (20°: 58.01% ± 23.10%; P = .0335), and peak force after 6-mm resection (60°: 60.67% ± 9.29%; P < .001) (20°: 74.44% ± 9.84%; P = .007).

CONCLUSION

Resecting more than 4 to 6 mm of the acetabular rim during hip arthroscopic surgery to address a pincer deformity may dramatically increase contact pressures by 3-fold at the acetabular base. The study suggests that excessive rim resection may lead to increased loads in the hip joint and may predispose to premature joint degeneration.

CLINICAL RELEVANCE

Resecting more than 4 to 6 mm of the acetabular rim may significantly alter hip joint biomechanics, increasing joint reactive forces and subsequent chondrolabral degeneration.

The effect of acetabular rim recession on anterior acetabular coverage: a cadaveric study using the false-profile radiograph

BACKGROUND

The majority of rim recession for femoroacetabular impingement (FAI) is performed anteriorly and has traditionally been assessed by the lateral center-edge (CE) angle, which correlates most closely with lateral coverage. The radiographic false-profile view permits measurement of anterior coverage via the anterior CE angle and more closely correlates with anterior coverage.

PURPOSE

To answer the following questions: (1) How does incremental anterior rim recession change lateral and anterior CE angles? and (2) Can these changes be predicted by a formula?

STUDY DESIGN

Descriptive laboratory study.

METHODS

Twelve cadaveric hips were dissected free of soft tissue to expose the anterior acetabular rim. Incremental resections of 2.5 mm (range, 0-10 mm) were performed from the 12- to 3-o'clock position using a Dremel rotary tool. Anteroposterior hip and false-profile radiographs were obtained at each interval using a fluoroscopic C-arm. The lateral and anterior CE angles were measured by 3 orthopaedic surgeons.

RESULTS

The average preresection lateral CE angle was 35.1°, and the mean decrease in lateral CE angle from 0 to 10 mm was 9.9°; the average preresection anterior CE angle was 38.4° and the mean decrease in anterior CE angle from 0 to 10 mm was 18.2°. The anterior CE angle decreased by a factor of 1.9 when compared with the lateral CE angle (P = 2 × 10(-7)). The lateral CE angle decreased by approximately 1° (1.0°) per millimeter of rim recessed. The anterior CE angle decreased by approximately 2° (1.8°) per millimeter of rim recessed.

CONCLUSION

The lateral CE angle should not be extrapolated to reflect anterior acetabular coverage. The anterior CE angle is a superior marker and predictably decreases with rim recession at double the rate of the lateral CE angle.

CLINICAL RELEVANCE

The false-profile view is recommended in the perioperative workup for all patients undergoing arthroscopic treatment of pincer impingement.

Does femoral rotation influence anteroposterior alpha angle, lateral center-edge angle, and medial proximal femoral angle? A pilot study

BACKGROUND

Femoral rotation on AP radiographs affects several parameters used to assess morphologic features of the proximal femur but its effect on femoroacetabular impingement parameters remains unknown.

QUESTION/PURPOSES

We therefore evaluated and characterized the potential effect of femoral rotation on (1) AP alpha angle, (2) lateral-center edge angle (LCEA), and (3) medial proximal femoral angle (MPFA) on AP hip radiographs.

METHODS

We took seven AP hip radiographs at intervals of successive femoral rotation on a single dry, cadaveric specimen: 60°, 40°, and 20° internal rotation; 0° neutral/anatomic rotation; and 20°, 40°, and 50° external rotation. The AP alpha angle, LCEA, and MPFA were measured on all radiographs by two independent evaluators.

RESULTS

Within the range of femoral rotation studied, the AP alpha angle ranged from 39° to 62°, the LCEA from 25° to 35°, and the MPFA from 70° to 115°. MPFA and AP alpha angle showed a linear relationship with femoral rotation. Each additional degree of internal rotation produced a reciprocal reduction of the MPFA by 0.36° and the AP alpha angle by 0.18° and vice versa in external rotation. The LCEA, especially within the internal rotation range, showed minimal variation.

CONCLUSIONS

These changes in radiographic parameters emphasize the importance of femoral rotation and patient positioning. We recommend radiographs be evaluated for excessive femoral rotation or nonstandardized positioning before interpretation for diagnostic and treatment implications. It may be prudent to repeat radiographs in these circumstances or, when standardized positioning is not feasible, proceed toward advance imaging.

New radiographic parameters to describe anterior acetabular rim trimming during hip arthroscopy

PURPOSE

The purpose of this study was to describe additional radiographic parameters that may detect changes within the acetabular cavity during acetabular rim trimming for pincer-type femoroacetabular impingement.

METHODS

Cadaveric hips that met the inclusion criteria were stripped of all tissue and had a portion of their labra removed; 5 mm of anterior acetabulum was measured in the 12- to 3-o'clock position and resected with a Dremel device (Robert Bosch Tool, Mount Pleasant, IL). Anteroposterior radiographs were obtained with a C-arm image intensifier. Radiographic measurements were subsequently obtained using the anterior rim angle (ARA), anterior wall angle (AWA), and anterior margin ratio (AMR).

RESULTS

Statistically significant changes were seen in the ARA, AWA, and AMR. Mean pre- and post-trimming changes were 81.0° and 85.7°, respectively, for the ARA; 34.8° and 29.2°, respectively, for the AWA; and 0.66 and 0.57, respectively, for the AMR.

CONCLUSIONS

Although much attention has been focused on the center-edge angle, the anterior aspect of the acetabulum has not previously been characterized. In conjunction with the center-edge angle and Tönnis angle, the new parameters of ARA, AWA, and AMR can be used to provide a more comprehensive description of the acetabulum. The ARA, AWA, and AMR can be used to guide the surgeon intraoperatively and postoperatively in further clarifying acetabular morphology and in determining whether the rim resection was adequate. This study determined that there exist new radiographic parameters with significant changes in the anterior acetabulum as quantified by the ARA, AWA, and AMR that can be used to describe the radiographic changes after acetabular rim resection.

CLINICAL RELEVANCE

The new parameters of ARA, AWA, and AMR can be used to provide a more comprehensive description of the acetabulum. These radiographic measurements can also be used by hip arthroscopists to better describe their surgical contribution to anterior rim trimming.

Arthroscopic labral reconstruction with gracilis autograft

Despite growing interest in hip arthroscopy and labral preservation, some patients have severely damaged, degenerative, or deficient labrums and may be candidates for arthroscopic labral reconstruction. The ligamentum teres has been used as a graft source for open hip labral grafting, and the iliotibial band has been used in the arthroscopic setting. We present an alternative method of hip labral reconstruction using the gracilis autograft, which does not require post-harvest manipulation. Arthroscopic techniques for graft tensioning and labrum-graft overlap are introduced that may facilitate restoration of labral function in patients with otherwise non-salvageable labrums.

The clamshell fracture and adjunctive acetabuloplasty in the arthroscopic osteosynthesis of femoral head fractures with femoroacetabular impingement

The clamshell fracture of the femoral head and its arthroscopic osteosynthesis are described. This suprafoveal osteochondral fracture may have folded onto itself during closed reduction of the associated anterior hip dislocation. The resultant fracture fragment had almost circumferential chondral coverage that required arthroscopic manipulation to "pry apart the clamshell," permitting arthroscopic reduction. This patient also had pre-existing silent femoroacetabular impingement, and the novel use of arthroscopic acetabuloplasty permitted internal fixation by improving the path for headless screw fixation. The arthroscopic techniques and clinical outcome at greater than 2 years are presented. Albeit rare, the clamshell fracture configuration should be recognized and may be amenable to successful arthroscopic osteosynthesis. Of broader clinical impact and application, adjunctive acetabuloplasty may permit the successful osteosynthesis of select femoral head fractures in patients with concurrent acetabular overcoverage by completely arthroscopic techniques that engage both the fracture fragment and the attractive benefits of less invasive surgery.