Inactivating PTH/PTHrP signaling disorders (iPPSDs): evaluation of the new classification in a multicenter large series of 544 molecularly characterized patients.

OBJECTIVE: Pseudohypoparathyroidism and related disorders belong to a group of heterogeneous rare diseases that share an impaired signaling downstream of Gsα-protein-coupled receptors. Affected patients may present with various combination of symptoms including resistance to PTH and/or to other hormones, ectopic ossifications, brachydactyly type E, early onset obesity, short stature and cognitive difficulties. Several years ago we proposed a novel nomenclature under the term of inactivating PTH/PTHrP signaling disorders (iPPSD). It is now of utmost importance to validate these criteria and/or improve the basis of this new classification. DESIGN: Retrospective study of a large international series of 459 probands and 85 relatives molecularly characterized. METHODS: Information on major and minor criteria associated with iPPSD and genetic results were retrieved from patient files. We compared the presence of each criteria according to the iPPSD subtype, age and gender of the patients. RESULTS: More than 98% of the probands met the proposed criteria for iPPSD classification. Noteworthy, most patients (85%) presented a combination of symptoms rather than a single sign suggestive of iPPSD and the overlap among the different genetic forms of iPPSD was confirmed. The clinical and molecular characterization of relatives identified familial history as an additional important criterion predictive of the disease. CONCLUSIONS: The phenotypic analysis of this large cohort confirmed the utility of the major and minor criteria and their combination to diagnose iPPSD. This report shows the importance of having simple and easily recognizable signs to diagnose with confidence these rare disorders and supports a better management of patients.

Development of heterotopic ossification after multiple-ligament reconstruction of the knee joint: Incidence and explanatory factor analysis.

BACKGROUND: The development of heterotopic ossification (HO) might nullify any benefit of multiple-ligament reconstruction of the knee joint. The purpose of this study was to investigate the incidence and the specific explanatory factors for the development of HO after multiple-ligament reconstruction of the knee joint. METHODS: From January 2011 to June 2016, 72 consecutive patients with knee dislocations received multiple-ligament reconstructions, of which 57 (79%) were available for a minimum follow up of 12 months and were included in this study. Anteroposterior (AP) and lateral radiographs were reviewed for all patients. This knee dislocation cohort was separated into two groups based on the presence or absence of HO for comparisons. In addition, the HO group was divided into three subgroups based on a modified quadrant grading system introduced by the senior author for further evaluation. Multivariate logistic regression analysis was then performed to identify specific explanatory factors predicting development of HO in patients after multiple-ligament reconstructions of the knee joint. RESULTS: Among the 72 consecutive patients, 57 (79%) were available for the clinical evaluations with an average period of 28.4 months (range, 12-51 months). Twenty-one patients (37%) showed radiological evidence of HO. The HO group (n = 21) showed significantly inferior results of knee flexion angle compared with the non-HO group (n = 36) (HO group vs. non-HO group: 124 ± 13° vs. 132 ± 5°; P<0.01). According to the quadrant grading system, there were seven patients with grade I, nine with grade II, and five with grade III HO. Subgroup analysis further revealed that higher HO grade would lead to lower knee flexion angle. In addition, multivariate regression analysis showed that concomitant posterior cruciate ligament reconstruction was the only independent explanatory factor predicting the development of HO after multiple-ligament reconstruction of the knee joint (P=0.018; odds ratio, 8.75; 95% confidence interval, 1.69-39.7). CONCLUSION: In this cohort of knee dislocations, the incidence of HO development following multiple-ligament reconstruction was 37%, with grade III HO showing the most inferior range of motion outcome. Moreover, concomitant posterior cruciate ligament reconstruction was the only independent predictor for the development of HO.

Long-term results of Zweymüller SLL femoral stem in revision hip arthroplasty for stage II and IIIA femoral bone defect: a 9-15-year follow-up study.

BACKGROUND: Loosening of femoral stem can be associated with a wide spectrum of bone loss that represents the most important factor for choosing the most appropriate revision implant. Positive outcomes in femoral revision were already observed with Zweymüller Alloclassic® SLL stem in short- and medium-term follow-up. The aim of the study is to analyse the clinical results of 31 patients who underwent prosthetic revision for aseptic loosening of femoral component with Zweymüller femoral stem and long follow-up. METHODS: The series included 10 men and 21 women with a mean age of 66.24 years at the time of revision surgery and a mean follow-up of 12.25 years. Clinical and radiological evaluation was performed at 2 months, 6 months and yearly, using Harris Hip Score (HHS) and Engh's criteria and Brooker classification for heterotopic ossifications. RESULTS: At the last follow-up, the survival of the stem was observed in all patients (32 hips). The mean HHS was 77.83 ± 20.90. Clinical results were stated as excellent in 14 cases, good in 5 cases, fair in 4 cases and poor in 9 cases. Radiographic stability with fixation by bone ingrowth was observed in 15 cases and with fibrous ingrowth in 17 cases. Heterotopic ossifications grade III was observed in 4 cases and grade II in 3 cases. CONCLUSIONS: Zweymüller Alloclassic® SLL stem showed excellent or good results in about 59% of revision surgery for aseptic loosening. The survival rate of the stem at 9-15 years of follow-up was satisfactory.

A patient with conventional and follicular variant papillary thyroid microcarcinoma and Eagle's syndrome, Langlais type III, with hyoid bone variation.

AIM: Presenting an extraordinary case of Eagle's syndrome (ES) with the classical and follicular variant of papillary thyroid microcarcinoma (PTmC) and an uncommon stylohyoid ligament calsification, aside from O'Carroll's System. CASE REPORT: A 52-year-old Turkish man with an histopathology of the follicular variant of PTmC (FVPTmC) of his right lobe and conventional PTmC of his left lobe of the thyroid with an adjuvant 100 mCi radioactive iodine (RAI) ablation was admitted. On the routine follow-up of the present case, a lineer structure at the 3rd compartment of neck in his ultrasonography, a styloid ligament calsification in his noncontrast computed tomography (CT), and a left styloid process of the temporal bone of 29 mm in size in his three-dimensional (3D) CT scanning had been revealed. Conclusively, an ES, Langlais Type III with The Calcification Pattern IV, was recognized. DISCUSSION: A noninvasive peroral medical management was administered as a first-line treatment for the neuropathic sequelae of ES and it has provided relief of signs and symptoms without any recurrence to date, for three years and three months. CONCLUSION: To our knowledge, it is an highly extreme and first case of ES in the English literature, recognized in the course of his programmed follow-up of his conventional PTmC and FVPTmC, simultaneously possessing an exceptional stylohyoid ligament calsification, apart from O'Carroll's System, even with an anatomic variation of the hyoid bone. KEY WORDS: Eagle's Syndrome Follicular variant of papillary thyroid microcarcinoma, Hyoid bone variation, Langlais classification, O'Carroll's System, Radioactive iodine, Papillary thyroid microcarcinoma.

Inactivating PTH/PTHrP Signaling Disorders.

Pseudohypoparathyroidism (PHP), pseudo-PHP, acrodysostosis, and progressive osseous heteroplasia are heterogeneous disorders characterized by physical findings, differently associated in each subtype, including short bones, short stature, a stocky build, ectopic ossifications (features associated with Albright's hereditary osteodystrophy), as well as laboratory abnormalities consistent with hormone resistance, such as hypocalcemia, hyperphosphatemia, and elevated parathyroid hormone (PTH) and thyroid-stimulating hormone levels. All these disorders are caused by impairments in the cAMP-mediated signal transduction pathway and, in particular, in the PTH/PTHrP signaling pathway: the main subtypes of PHP and related disorders are caused by de novo or autosomal dominantly inherited inactivating genetic mutations, and/or epigenetic, sporadic, or genetic-based alterations within or upstream of GNAS, PRKAR1A, PDE4D, and PDE3A. Here we will review the impressive progress that has been made over the past 30 years on the pathophysiology of these diseases and will describe the recently proposed novel nomenclature and classification. The new term "inactivating PTH/PTHrP signaling disorder," iPPSD: (1) defines the common mechanism responsible for all diseases, (2) does not require a confirmed genetic defect, (3) avoids ambiguous terms like "pseudo," and (4) eliminates the clinical or molecular overlap between diseases.

Incidence and morphometry of caroticoclinoid foramina in Greek dry human skulls.

BACKGROUND: Ossification of the caroticoclinoid ligament (CCL) and formation of a caroticoclinoid foramen (CCF) may impose significant risk to neurosurgeons by impeding mobilization of the cavernous segment of the internal carotid artery. Although safe surgical access to the clinoidal space is related to understanding the CCF anatomical and ethnic variants, there remains a paucity of studies of the morphology and bony relationships. The current study provides a systematic morphological and morphometric analysis of the CCF, the ossification of the CCL extending between the anterior and middle clinoid processes, and their relations in a Greek population. MATERIALS AND METHODS: The incidence of unilateral and bilateral CCF, types (complete, incomplete, and contact) of ossified CCLs, and foramina diameter according to side and gender were determined in 76 Greek adult dry skulls. Findings were correlated with the morphology of optic strut (OS) (presulcal, sulcal, postsulcal, and asymmetric). RESULTS: A CCF was detected in 74% of the specimens. The majority of skulls (51.4%) had bilateral CCF, whereas 22.3% of the skulls had unilateral foramina. Incomplete CCF were observed in 69.3%, complete in 19.8%, and contact type in 10.9%. The mean CCF diameter was 0.55 ± 0.07 cm on the left and 0.54 ± 0.08 cm on the right side. Side symmetry existed, although there were no significant differences according to gender. The CCF were more prominent in skulls with a sulcal type of OS. CONCLUSIONS: The results of the present study augment the current knowledge on the morphology of key anatomical landmarks, CCF, and CCL ossification in the sellar area, indicating population differences. A significant side asymmetry in caroticoclinoid osseous bridging and foramina is highlighted. These findings are necessary for a safe surgical access to the clinoidal area.

An Analysis of Paravertebral Ossification in Cervical Artificial Disc Replacement: A Novel Classification Based on Computed Tomography.

OBJECTIVE: Cervical artificial disc replacement (CADR) is a new technology in cervical spine surgery. However, CADR may result in paravertebral ossification (PO) after surgery and affect the mobility of the related spinal segments. The present widely used assessment method based on X-ray tomography cannot provide the position information of PO, and also PO detection rates by X-ray are low. The incidence of PO varies dramatically between studies. This study built a novel classification system based on cervical computer tomography (CT) scan to re-evaluate the incidence of PO and its influence on CADR, and also analyzed the predisposing factors of PO. METHODS: In this retrospective study, 71 patients (from January 2004 to December 2009) who received cervical artificial disc replacement in our hospital were enrolled, and 82 cervical segments were replaced by Bryan discs. The range of motion (ROM) of the related cervical segments and scores of neurological symptoms (neck disability index [NDI] and Japanese Orthopaedic Association [JOA] scores) for both pre-surgery and last follow-up were acquired, respectively. After the establishment of a novel grading system for PO based on CT scan, we analyzed the CT images acquired before surgery and at the last time follow-up. Occurrence and distribution of PO at both time points were calculated. ROM between pre-surgery and post-surgery was compared by paired t-test stratified by PO stages. One-way ANOVA was used to compare NDI and JOA scores between high-grade and low-grade PO groups after surgery. The χ2 -test was used to evaluate the risk (odds ratio) of predisposing factors in developing high-grade PO after surgery. RESULTS: The CT-based classification system has good inter-observer and intra-observer reliability. The detection rate of PO by CT scan is higher than for traditional X-ray examination. The incidence of low-grade PO in all 82 segments at last follow-up is 32.9%. The occurrences of high-grade PO at preoperational and last follow-up time are 15.9% and 67.1%, respectively. The high-grade PO is mainly distributed around the uncovertebral joint. The pre-surgery and post-surgery ROM are similar in patients with low-grade PO at last follow-up time (9.80° ± 3.65° vs 10.03° ± 3.73°, P = 0.801); however, in patients with high-grade PO the post-surgery ROM decreases significantly compared to the pre-surgery ROM (9.73° ± 4.03° vs 6.63° ± 4.21°, P < 0.001). There is no statistical difference for JOA and NDI scores after surgery between high-grade and low-grade PO patients at final follow-up (P = 0.264, P = 0.703). The χ2 -test indicates that patients with preoperational existence of PO have a high risk of high-grade PO after surgery (OR = 4, P = 0.012). CONCLUSIONS: The novel CT image-based PO classification system has good intra-observer reliability. The incidence of PO after Bryan cervical disk replacement is relative high, and the high-grade PO is mainly distributed at the uncovertebral joint. The high-grade PO will affect the ROM after surgery; however, it does not affect the neurologic symptoms.

Eagle syndrome: a narrative review / Síndrome de Eagle: una revisión narrativa

Abstract: painful disorders in the maxillofacial region are common in dental practice. Most of these conditions are not properly diagnosed because of inadequate knowledge of craniofacial and cervico-pharyngeal syndromes such as Eagle Syndrome. The aim of this review is to describe the general aspects, diagnosis and treatment of Eagle syndrome. Eagle syndrome or stylohyoid syndrome was first described by Watt W. Eagle in 1937. It was defined as orofacial pain related to the elongation of the styloid process and ligament stylohyoid calcification. The condition is accompanied by symptoms such as dysphonia, dysphagia, sore throat, glossitis, earache, tonsillitis, facial pain, headache, pain in the temporomandibular joint and inability to perform lateral movements of the neck. Diagnosis and treatment of Eagle syndrome based on symptoms and radiographic examination of the patient will determine the need for surgical or nonsurgical treatment. Eagle syndrome is a complex disorder demanding a thorough knowledge of its signs and symptoms to make a correct diagnosis and provide an appropriate subsequent treatment. Disseminating information about this syndrome among medical-dental professionals is essential to provide adequate dental care to patients.

Resumen: en la práctica odontológica, es frecuente encontrar alteraciones con sintomatología dolorosa en la región maxilofacial, las cuales no son apropiadamente diagnosticadas, a causa del desconocimiento de síndromes craneofaciales y cervicofaríngeos, como el Síndrome de Eagle. El objetivo de esta revisión es describir los aspectos generales, diagnóstico y tratamiento del Síndrome de Eagle. El Síndrome de Eagle o estilalgia es la entidad nosológica, descrita por Watt W. Eagle en 1937, definida como aquel dolor orofacial relacionado con la elongación de la apófisis estiloides y calcificación del ligamento estilohioideo; el cual está acompañado de síntomas como: disfonía, disfagia, dolor faríngeo, glositis, otalgia, tonsilitis, dolor facial, cefalea, odinofagia, dolor en la articulación temporomandibular e imposibilidad de realizar movimientos laterales del cuello. El diagnóstico y tratamiento del Síndrome de Eagle está basado en la sintomatología y el examen radiográfico del paciente, lo cual determinará el tratamiento quirúrgico o no quirúrgico. El Síndrome de Eagle es una patología compleja que requiere un conocimiento amplio de sus signos y síntomas, para establecer un correcto diagnóstico y posteriormente un adecuado tratamiento. Para ello, es necesario difundir la información sobre este síndrome entre los profesionales médico-odontológico y así brindar una atención adecuada a cada uno de los pacientes.

From pseudohypoparathyroidism to inactivating PTH/PTHrP signalling disorder (iPPSD), a novel classification proposed by the EuroPHP network.

OBJECTIVE: Disorders caused by impairments in the parathyroid hormone (PTH) signalling pathway are historically classified under the term pseudohypoparathyroidism (PHP), which encompasses rare, related and highly heterogeneous diseases with demonstrated (epi)genetic causes. The actual classification is based on the presence or absence of specific clinical and biochemical signs together with an in vivo response to exogenous PTH and the results of an in vitro assay to measure Gsa protein activity. However, this classification disregards other related diseases such as acrodysostosis (ACRDYS) or progressive osseous heteroplasia (POH), as well as recent findings of clinical and genetic/epigenetic background of the different subtypes. Therefore, the EuroPHP network decided to develop a new classification that encompasses all disorders with impairments in PTH and/or PTHrP cAMP-mediated pathway. DESIGN AND METHODS: Extensive review of the literature was performed. Several meetings were organised to discuss about a new, more effective and accurate way to describe disorders caused by abnormalities of the PTH/PTHrP signalling pathway. RESULTS AND CONCLUSIONS: After determining the major and minor criteria to be considered for the diagnosis of these disorders, we proposed to group them under the term 'inactivating PTH/PTHrP signalling disorder' (iPPSD). This terminology: (i) defines the common mechanism responsible for all diseases; (ii) does not require a confirmed genetic defect; (iii) avoids ambiguous terms like 'pseudo' and (iv) eliminates the clinical or molecular overlap between diseases. We believe that the use of this nomenclature and classification will facilitate the development of rationale and comprehensive international guidelines for the diagnosis and treatment of iPPSDs.

Heterotopic ossification of the long head of the triceps after reverse total shoulder arthroplasty.

BACKGROUND: Heterotopic ossification (HO) around shoulder arthroplasty is a frequent finding with unclear clinical relevance. This study evaluated the incidence, relevance, and predisposing factors of HO in the long head of the triceps tendon after reverse shoulder arthroplasty. METHODS: Retrospective chart review was conducted to identify patients who had a reverse shoulder arthroplasty performed between 2008 and 2012. Patient demographics, implant types, and diagnoses were noted. Three fellowship-trained shoulder/elbow surgeons independently evaluated postoperative Grashey radiographs using a novel classification system. RESULTS: Within a 164-patient cohort, the overall HO rate in the long head of the triceps tendon was 61.6%; 23.2% of osteophytes were considered impinging, 14.6% had notching, 14.0% were free-floating, and 3.0% appeared ankylosed. Although not statistically significant, revision surgery had a higher rate of HO (68.3%) compared with primary surgery (59.4%). There was no difference in HO rates between diagnoses or implant types. Male and female HO rates were 74.0% and 56.1%, respectively (P = .0304). Between patients with and without HO, forward elevation was 121° compared with 133° (P = .0087) and external rotation was 19° compared with 25° (P = .0266); however, HO size did not significantly affect motion. CONCLUSIONS: Using our novel classification scheme, HO was a common finding in this series. Men had a higher rate of HO formation, and HO formation was associated with worse postoperative motion. Further study is needed to fully characterize the clinical implications of HO involving the long head of the triceps tendon and to explore potential preventive measures.

Ethnic differences in heterotopic ossification following total hip arthroplasty.

AIMS: We aimed to assess the influence of ethnicity on the incidence of heterotopic ossification (HO) after total hip arthroplasty (THA). PATIENTS AND METHODS: We studied the six-month post-operative anteroposterior radiographs of 1449 consecutive primary THAs (1324 patients) and retrospectively graded them for the presence of HO, using the Brooker Classification. RESULTS: Based on multivariate analysis, African-American ethnicity was an independent risk factor for HO formation following THA with an adjusted odds ratio (OR) of 2.6 (95% confidence interval (CI) 1.3 to 5.2, p = 0.007) for severe HO and 1.9 (95% CI 1.3 to 2.7, p < 0.001) for any grade of HO. CONCLUSION: Given the increased risk of HO formation, particularly high grade HO, and the potentially poorer outcomes associated with HO, it is important to consider using prophylaxis against HO in patients of African-American ethnicity undergoing THA. TAKE HOME MESSAGE: African Americans are at an increased risk for developing heterotopic ossification and thus may benefit from HO prophylaxis. Cite this article: Bone Joint J 2016;98-B:761-6.

A new classification of peri-articular heterotopic ossification of the hip associated with neurological injury: 3D CT scan assessment and intra-operative findings.

In this paper we propose a new classification of neurogenic peri-articular heterotopic ossification (HO) of the hip based on three-dimensional (3D) CT, with the aim of improving pre-operative planning for its excision. A total of 55 patients (73 hips) with clinically significant HO after either traumatic brain or spinal cord injury were assessed by 3D-CT scanning, and the results compared with the intra-operative findings. At operation, the gross pathological anatomy of the HO as identified by 3D-CT imaging was confirmed as affecting the peri-articular hip muscles to a greater or lesser extent. We identified seven patterns of involvement: four basic (anterior, medial, posterior and lateral) and three mixed (anteromedial, posterolateral and circumferential). Excellent intra- and inter-observer agreement, with kappa values > 0.8, confirmed the reproducibility of the classification system. We describe the different surgical approaches used to excise the HO which were guided by the 3D-CT findings. Resection was always successful. 3D-CT imaging, complemented in some cases by angiography, allows the surgeon to define the 3D anatomy of the HO accurately and to plan its surgical excision with precision.

Effect of heterotopic ossification on hip range of motion and clinical outcome.

The utility of heterotopic ossification (HO) classification systems is debatable. The range of motion and Harris hip score (HHS) were calculated in 104 patients with known HO after total hip arthroplasty and 208 matched controls without HO. The patients with HO were radiographically divided into high and low grade HO groups. There was no statistically significant association of HHS with high or low grade HO. High grade HO had a statistically significant 6° loss of terminal hip flexion, 4° loss of abduction, and 6° loss of internal rotation at the hip. The small changes in terminal hip range of motion and lack of association with HHS may be the result of false radiographic continuity resulting in an overestimation of the disability in high grade HO.

[Radiation therapy for heterotopic ossification prophylaxis].

Heterotopic ossification (HO) is a well-known condition of bone formation in soft tissues due to trauma (e.g. surgery) or neurological injury, but the exact aetiology is unknown. In most cases, HO is asymptomatic, but it may cause pain, reduced mobility of joints, and loss of functioning. Various patient groups have a significant risk of developing HO after surgery and should be offered prophylactic treatment. Nonsteroidal anti-inflammatory drugs and radiotherapy are internationally accepted treatments. This review discusses the potential for radiotherapy as prophylaxis against HO.

Osificación hetertópica neurogénica bilateral de cadera / Bilateral neurogenic heterotopic ossification of hip

La osificación heterotópica es una verdadera actividad osteoblástica con formación anormal de hueso lamelar maduro en tejidos blandos extraesqueléticos donde el hueso no existe normalmente. Se presenta un paciente con afección de ambas caderas, pretendiendo realizar una breve revisión sobre diagnóstico, seguimiento y tratamiento de esta patología.

Evaluation of elongated styloid process on digital panoramic radiographs.

BACKGROUND AND OBJECTIVE: The elongated styloid process may produce characteristic head and neck pain syndromes, commonly known as Eagle's syndrome. An awareness of this syndrome is important to all health practitioners involved in the diagnosis and treatment of neck and head pain. It has been estimated that 2 to 28% of the general adult population has radiographic appearance of elongated styloid process. The objective of the study was to assess the elongation of styloid process on digital panoramic radiographs and to evaluate the prevalence of elongation according to age, sex and types. RESULTS: Elongated styloid process was seen in 107 subjects out of 300 patients who were aged between 10 and 70 years old. Our study revealed that as age increased elongation of styloid process increased with female predominance. Type 1 elongation was most common than the other types of elongation. We also found that left styloids were elongated than the right with bilateral elongation. CONCLUSION: Panoramic radiographs can show a correct picture of elongated styloid process which can confirm the diagnosis and can thus help avoid misinterpretation of the symptoms as tonsillar pain or pain of dental, pharyngeal or muscular origin and hence panoramic radiography is economical and the best imaging modality to view the elongation of styloid process.

A classification method for neurogenic heterotopic ossification of the hip.

BACKGROUND: Existing classifications for heterotopic ossification (HO) do not include all HO types; nor do they consider the anatomy of the involved joint or the neurological injury. Therefore, we performed this study to propose and evaluate a classification according to the location of neurogenic HO and the neurological injury. MATERIALS AND METHODS: We studied the files of 24 patients/33 hips with brain or spinal cord injury and neurogenic HO of the hip treated with excision, indomethacin, and radiation therapy. We classified patients according to the Brooker classification scheme as well as ours. Four types of neurogenic HO were distinguished according to the anatomical location of HO: type 1, anterior; type 2, posterior; type 3, anteromedial; type 4, circumferential. Subtypes of each type were added based on the neurological injury: a, spinal cord; b, brain injury. Mean follow-up was 2.5 years (1-8 years). RESULTS: The Brooker classification scheme was misleading-all hips were class III or IV, corresponding to ankylosis, even though only 14 hips had ankylosis. On the other hand, our classification was straightforward and easy to assign in all cases. It corresponded better to the location of the heterotopic bone, and allowed for preoperative planning of the appropriate surgical approach and evaluation of the prognosis; recurrence of neurogenic HO was significantly higher in patients with brain injury (subtype b), while blood loss was higher for patients with anteromedial (type 3) and circumferential (type 4) neurogenic HO. CONCLUSIONS: Our proposed classification may improve the management and evaluation of the prognosis for patients with neurogenic HO.

The incidence of heterotopic ossification after hip arthroscopy.

BACKGROUND: Minimally invasive techniques to treat femoroacetabular impingement (FAI), snapping hip syndrome, and peritrochanteric space disorder (PSD) were developed to reduce complications and recovery time. Although a multitude of studies have reported on the incidence of heterotopic ossification (HO) after open procedures of the hip, there is little known about the rate of HO after hip arthroscopy. HYPOTHESES: The incidence of HO after hip arthroscopy is comparable with that after open surgical dislocation of the hip and can be reduced with the addition of indomethacin to an existing nonsteroidal anti-inflammatory medication prophylaxis protocol. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: Between July 2008 and July 2010, 616 primary hip arthroscopies were performed to treat FAI and PSD. In July 2009, indomethacin was added in the acute postoperative period to an existing HO prophylactic protocol of naproxen administered for 30 days postoperatively. Postoperative radiographs were reviewed to detect the presence and classify the size and location of HO. Odds ratios and logistic regression explored predictor variables and their relationships with HO, with P < .05 defined as significant. RESULTS: Twenty-nine (21 male, 8 female) of 616 (4.7%) hip procedures developed HO postoperatively. Brooker classification of HO was 18 grade I, 4 grade II, 6 grade III, and 1 grade IV. Mean follow-up was 13.2 months (range, 2.9-26.5 months). Rate of HO for cases with and without indomethacin for prophylaxis was 1.8% (6/339) and 8.3% (23/277), respectively. This difference was statistically significant (P < .05), and patients who underwent protocol 1 were 4.36 times more likely to develop HO postoperatively than those who had protocol 2. The majority of cases of HO (72.4%) occurred in male patients, and all cases occurred in the setting of osteoplasty performed for symptomatic FAI. We were not able to demonstrate statistically significant clinical risk factors that were predictive for the development of postoperative HO. However, the data clearly demonstrate that the performance of arthroscopic osteoplasty with a capsular cut in male patients represented the majority of cases, who are likely the group at highest risk. Seven cases (~1%) required revision procedures to excise HO. There were no cases of recurrence of HO after excision, whether it was performed open or arthroscopically. CONCLUSION: The addition of indomethacin is effective in reducing the incidence of HO after hip arthroscopy and should be especially considered in male patients who undergo osteoplasty for correction of symptomatic FAI.