Hip Dysplasia Research

Developmental dysplasia of the hip (DDH, or hip dysplasia, is a developmental condition that occurs during the growth of the hip joint, over the first 1-2 decades of life. Hip dysplasia describes a shallow acetabulum or hip socket that is insufficiently deep to adequately cover the femoral head. This insufficient coverage creates abnormal hip loading mechanics where the bone and cartilage at the edge of the acetabulum see very high loading forces during weight-bearing activities such as standing and walking. If hip dysplasia is left untreated, these high loads at the rim of the socket cause the hip’s cartilage and labrum to break down, causing pain, decreased function, and eventually hip osteoarthritis.

Hip dysplasia is the most common pediatric hip condition – about 1 in 6 newborns will have hip instability and about 3 in 1,000 will require surgery for hip dysplasia. Hip dysplasia can result in pain and dysfunction starting in childhood through young adulthood, and is the leading cause of early-onset hip osteoarthritis before the age of 60 years. The poor prognosis of hip dysplasia warrants careful attention towards early identification and intervention in these hips with anatomical risk factors for mechanical misbehavior. Our research is focused on the proper screening, diagnosis, treatment, and prevention of hip dysplasia to provide the best patient care and improve the quality of life for those affected.

Clinical Associate Professor, Orthopaedic Surgery


  • No Delay in Age of Crawling, Standing or Walking with Pavlik Harness Treatment: A Prospective Cohort Study. The Journal of the American Academy of Orthopaedic Surgeons Stavinoha, T. J., Pun, S. Y., McGlothlin, J. D., Uzosike, M. B., Segovia, N. A., Imrie, M. N. 2023


    BACKGROUND: Pavlik harness treatment is the standard of care for developmental dysplasia of the hip in infants younger than 6 months. The effect of Pavlik harness treatment on the achievement of motor milestones has not previously been reported.METHODS: In this prospective cohort study, 35 patients were prospectively enrolled to participate and received questionnaires with sequential clinical visits monitoring treatment of their developmental dysplasia of the hip. One-sample Student t-tests assessed differences in milestone attainment age, and the Benjamini-Hochberg procedure was conducted to decrease the false discovery rate. Post hoc power analyses of each test were conducted. The age of achievement of eight early motor milestones were recorded and compared with a previously published cohort of healthy infants.RESULTS: Infants treated with a Pavlik harness achieved four early motor milestones markedly later than the reported age of achievement in a historical control group. These milestones included "roll supine" (5.3 vs. 4.5 months; P = 0.039), "roll prone" (5.7 vs. 5.0 months; P = 0.039), "sit" (6.4 vs. 5.2 months; P < 0.001), and "crawl on stomach" (7.7 vs. 6.6 months; P = 0.039). However, there was no difference in time to achievement of later motor milestones of "crawl on knees," "pull to stand," and "independent walking."CONCLUSION: Several early motor milestones were achieved at a statistically significantly later time than historical control subjects not treated in a Pavlik harness. Despite statistical significance, the small delays in early motor milestones were not thought to be clinically significant. No differences were observed in the later motor milestones, including knee crawling, standing, and independent walking. Clinicians and parents may be reassured by these findings.LEVEL OF EVIDENCE: Therapeutic Level II-prospective study.

    View details for DOI 10.5435/JAAOS-D-21-00249

    View details for PubMedID 37862341

  • Association of Hip Dysplasia With Trochlear Dysplasia in Skeletally Mature Patients. Orthopaedic journal of sports medicine Fithian, A. T., Richey, A. E., Sherman, S. L., Shea, K. G., Pun, S. Y. 2023; 11 (10): 23259671231200805


    Developmental dysplasia of the hip (DDH) and trochlear dysplasia (TD) are distinct pathologies with several important features in common. In addition to shared risk factors, both forms of dysplasia cause abnormal joint kinematics and force transmission, predisposing patients to pain, injuries to cartilage and soft tissue stabilizers, and ultimately arthritis.To evaluate for an association between hip dysplasia and TD in skeletally mature patients with symptomatic hip dysplasia.Cross-sectional study; Level of evidence, 3.A total of 48 patients with DDH who underwent periacetabular osteotomy were compared with 48 sex-matched patients who underwent hip arthroscopy for femoroacetabular impingement (FAI) between July 2014 and February 2021. All patients were skeletally mature. The Tönnis angle and lateral center-edge angle were measured on preoperative pelvis radiographs. Femoral version, trochlear depth, lateral trochlear inclination (LTI), tibial tubercle-trochlear groove distance (TTTG-d), and posterior lateral condylar angle (PLCA) were measured on preoperative magnetic resonance imaging scans of the symptomatic hip and ipsilateral knee. Continuous variables were compared between the patient groups using 2-sample t tests. Interobserver reliability was measured using the intraclass correlation coefficient.Patients with DDH demonstrated a reduced trochlear depth compared with patients with FAI (3.6 vs 4.6 mm; P < .001). There were no differences between groups in femoral anteversion, LTI, TTTG-d, or PLCA. Two (4.2%) patients with FAI and 17 (35.4%) patients with DDH had a trochlear depth <3 mm (P < .001). One (2.1%) patient with FAI and 7 (14.6%) patients with DDH had an LTI <11° (P = .027). There was no difference between groups in frequency of a convex proximal trochlea, patient-reported ipsilateral knee pain, or ipsilateral knee procedures.Patients with DDH had reduced trochlear depth compared with patients with FAI, demonstrating a higher incidence of dysplastic trochlear features that may predispose patients to patellofemoral joint disease. Further research is needed to determine whether screening at-risk patients and treating TD will help to prevent symptomatic patellofemoral disease.

    View details for DOI 10.1177/23259671231200805

    View details for PubMedID 37822419

    View details for PubMedCentralID PMC10563471

  • Acetabular labral reconstruction with medial meniscal allograft: preliminary results of a new surgical technique. European journal of orthopaedic surgery & traumatology : orthopedie traumatologie Chen, M. J., Hollyer, I., Pun, S. Y., Bellino, M. J. 2021


    PURPOSE: Reconstruction of the acetabular labrum during femoroacetabular impingement (FAI) surgery is accepted when the labrum is deficient and irreparable. Here we describe a novel technique using fresh-frozen medial meniscal allograft for labral reconstruction during surgical hip dislocation for correction of pincer FAI due to acetabular overcoverage.METHODS: The results from seven hips (six patients) that underwent this procedure with 1 year minimum follow-up, and radiographs are presented.RESULTS: Six of the seven hips had improvements in pain, hip flexion, hip abduction, and Merle d'Aubigne-Postel scores. Only one patient with pre-existing osteoarthritis underwent reoperation with conversion to total hip arthroplasty. All digastric trochanteric osteotomies healed, and there were no cases of femoral head osteonecrosis or progression of Tonnis grades.CONCLUSIONS: The medial meniscus is a morphologically and clinically suitable option for labral reconstruction and effectively restores the hip fluid seal.

    View details for DOI 10.1007/s00590-021-02986-2

    View details for PubMedID 34028622

  • What Are the Early Outcomes of True Reverse Periacetabular Osteotomy for Symptomatic Hip Overcoverage? Clinical orthopaedics and related research Pun, S. Y., Hosseinzadeh, S., Dastjerdi, R., Millis, M. B. 2020


    BACKGROUND: Acetabular overcoverage is associated with pincer-type femoroacetabular impingement (FAI). A subtype of acetabular overcoverage is caused by a deep acetabulum with a negatively tilted acetabular roof, in which acetabular reorientation may be a preferable alternative to rim trimming to uncover the femoral head. We introduced the true reverse periacetabular osteotomy (PAO) in 2003, which in contrast to an anteverting PAO, also flexes and abducts the acetabulum relative to the intact ilium to decrease anterior and lateral femoral head coverage and correct negative tilt of the acetabular roof. To our knowledge, the clinical results of the true reverse PAO have not been evaluated.QUESTIONS/PURPOSES: For a group of patients who underwent reverse PAO, (1) Do patients undergoing reverse PAO demonstrate short-term improvement in pain, function, and hip ROM, and decreased acetabular coverage, as defined by lateral and anterior center-edge angle and Tonnis angle? (2) Are there identifiable factors associated with success or adverse outcomes of reverse PAO as defined by reoperation, conversion to THA, or poor patient-reported outcome scores? (3) Are there identifiable factors associated with early complications?METHODS: Between 2003 and 2017, two surgeons carried out 49 reverse PAOs in 37 patients. Twenty-five patients had unilateral reverse PAO and 12 patients had staged, bilateral reverse PAOs. To ensure that each hip was an independent data point for statistical analysis, we chose to include in our series only the first hip in the patients who had bilateral reverse PAOs. During the study period, our general indications for this operation were symptomatic lateral and anterior acetabular overcoverage causing FAI that had failed to respond to previous conservative or surgical treatment. Thirty-seven hips in 37 patients with a median (range) age of 18 years (12 to 41; interquartile range 16-21) were included in this retrospective study at a minimum follow-up of 2 years (median 6 years; range 2 to 17). Thirty-four patients completed questionnaires, 24 patients had radiographic evaluation, and 23 patients received hip ROM clinical examination. However, seven patients had not been seen in more than 5 years. The clinical and radiographic parameters of all 37 hips that underwent reverse PAO in 37 patients from a longitudinally maintained institutional database were retrospectively studied preoperatively and postoperatively. Adverse outcomes were considered conversion to THA or a WOMAC pain score greater than 10 at least 2 years postoperatively. Patient-reported outcomes, radiographic measurements, and hip ROM were evaluated preoperatively and at most recent follow-up using a paired t-test or McNemar test, as appropriate. Linear regression analysis was used to assess for identifiable factors associated with clinical outcomes. Logistic regression analysis was used to assess for identifiable factors associated with adverse outcomes and surgical complications. All tests were two-sided, and p values less than 0.05 were considered significant.RESULTS: At a minimum of 2 years after reverse PAO, patients experienced improvement in WOMAC pain (-7 [95% CI -9 to -5]; p < 0.001), stiffness (-2 [95% CI -3 to -1]; p < 0.001), and function scores (-18 [95% CI -24 to -12]; p < 0.001) and modified Harris Hip Score (mHHS) (20 [95% CI 13 to 27]; p < 0.001). The mean postoperative hip ROM improved in internal rotation (8° [95% CI 2° to 14°]; p = 0.007). Acetabular coverage, as defined by lateral center-edge angle (LCEA), anterior center-edge angle (ACEA), and Tonnis angle, improved by -8° (95% CI -12° to -5°; p < 0.001) for LCEA, -12° (95% CI -15° to -9°; p < 0.001) for ACEA, and 9° (95% CI 6° to 13°; p < 0.001) for Tonnis angle. The postoperative severity of radiographic arthritis was associated with worse WOMAC function scores such that for each postoperative Tonnis grade, WOMAC function score increased by 12 points (95% CI 2 to 22; p = 0.03). A greater postoperative Tonnis grade was also correlated with worse mHHS, with an average decrease of 12 points (95% CI -20 to -4; p = 0.008) in mHHS for each additional Tonnis grade. Presence of a positive postoperative anterior impingement test was associated with a decrease in mHHS score at follow-up, with an average 23-point decrease in mHHS (95% CI -34 to -12; p = 0.001). Nineteen percent (7 of 37) of hips had surgery-related complications. Four hips experienced adverse outcomes at final follow-up, with two patients undergoing subsequent THA and two with a WOMAC pain score greater than 10. We found no factors associated with complications or adverse outcomes.CONCLUSION: The early clinical and radiographic results of true reverse PAO compare favorably to other surgical treatments for pincer FAI, suggesting that reverse PAO is a promising treatment for cases of pincer FAI caused by global acetabular overcoverage. However, it is a technically complex procedure that requires substantial training and preparation by a surgeon who is already familiar with standard PAO, and it must be carefully presented to patients with discussion of the potential risks and benefits. Future studies are needed to further refine the indications and to determine the long-term outcomes of reverse PAO.LEVEL OF EVIDENCE: Level IV, therapeutic study.

    View details for DOI 10.1097/CORR.0000000000001549

    View details for PubMedID 33296152

  • Is Increased Acetabular Cartilage or Fossa Size Associated With Pincer Femoroacetabular Impingement? Clinical orthopaedics and related research Pun, S. Y., Hingsammer, A., Millis, M. B., Kim, Y. 2017; 475 (4): 1013-1023


    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.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.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.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).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.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.

    View details for DOI 10.1007/s11999-016-5063-1

    View details for PubMedID 27637612

  • Hip dysplasia in the young adult caused by residual childhood and adolescent-onset dysplasia. Current reviews in musculoskeletal medicine Pun, S. 2016; 9 (4): 427-434


    Hip dysplasia is a treatable developmental disorder that presents early in life but if neglected can lead to chronic disability due to pain, decreased function, and early osteoarthritis. The main causes of hip dysplasia in the young adult are residual childhood developmental dysplasia of the hip (DDH) and adolescent-onset acetabular dysplasia. These two distinct disease processes affect the growing hip during different times of development but result in a similar deformity and pathomechanism of hip degeneration. Routine screening for DDH and counseling regarding risks for acetabular dysplasia in families with a history of early hip osteoarthritis may allow early identification and intervention in these hips with anatomical risk factors for joint degeneration.

    View details for PubMedID 27613709

  • Review: femoroacetabular impingement. Arthritis & rheumatology Pun, S., Kumar, D., Lane, N. E. 2015; 67 (1): 17-27

    View details for DOI 10.1002/art.38887

    View details for PubMedID 25308887

    View details for PubMedCentralID PMC4280287

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Dr. Stephanie Pun

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