Painful knee.

INTRODUCTION: A bipartite patella is a rare anatomical variant of the patella. A patella bipartite is often asymptomatic and is often an incidental finding on radiological imaging. The patella remains bipartite when secondary ossification centers fail to fuse. Herein, a case of bipartite patella improved after knee arthroscopy and surgical removal. PRESENTATION OF THE CASE: A 57-year-old male with a history of polytrauma. He complained of progressive pain in the right knee area. A radiological investigation reported a right bipartite patella. The condition improved after the open removal of the accessory patella. DISCUSSION: This case is considered type III according to Saupe's classification. Due to its location and radiological appearance, it is a painful synchondrosis of a bipartite patella. CONCLUSION: After the failure of conservative management, the removal of the bipartite patella was necessary and unavoidable to restore everyday activities.

Multipartite patella: A review of diagnostic techniques and management of the symptomatic patient.

Multipartite patella is an anatomical variant classified by the fragmentation of the main patellar body. The cause of this variant is due to failure in fusion of the patellar ossification centers. It is commonly misdiagnosed as a fracture of the patella in clinical practice, leading to unnecessary treatment measures. The aim of this review is to provide an overview of the development and classification of this variation, diagnostic imaging techniques, and assess the optimal management technique for the symptomatic patient. Multiple radiographic methods are used to identify this variant, with recent studies highlighting high sensitivity rates for nonradiative methods (ultrasound). In terms of symptomatic management, accessory fragment excision and vastus lateralis release provide the greatest alleviation of symptoms, with screw fixation being less favorable.

Accessory fragment migration in a professional baseball player with bipartite patella: A case report.

INTRODUCTION: Bipartite patella (BP) is usually recognized as an incidental radiographic finding. Therefore, no reports have observed the process of accessory fragment migration. We present the case of a professional baseball pitcher with significant migration of the fragment during follow-up. PRESENTATION OF CASE: A 26-year-old man was diagnosed with symptomatic BP and underwent conservative therapy. Eleven months later, he was unable to play baseball because of gradually worsening knee pain without obvious trauma. On radiographs, the accessory fragment which had located at the superolateral pole 11 months earlier migrated posterolaterally. The diagnosis of Saupe's type III BP was established, and open excision of the accessory fragment was performed. Postoperatively, full-weight-bearing walking and range-of-motion exercises were started the day after surgery. Three months after surgery, he could pitch with all his power without pain. DISCUSSION: Since our patient was a professional baseball right-handed pitcher who needed to step strongly on his left knee during pitching, strong traction force from the vastus lateralis was likely to have been repeatedly applied to the accessory fragment. It might lead to migration of the accessory fragment. The open excision of the accessory fragment was performed because the accessory fragment had migrated away from the patella body. CONCLUSION: We report a case of professional baseball player with symptomatic BP, in which case the chronological migration of the accessory fragment was observed without obvious trauma. When the accessory fragment is identified without obvious trauma, one of the differential diseases could be a BP.

Stress Injuries of the Knee.

Stress injuries to the bone and physis of the knee are common in the active adolescent patient and can be broken down into bone stress injuries (BSIs) and chronic physeal stress injuries. BSIs result from prolonged, repetitive bone loading, whereas chronic physeal stress injuries develop from repetitive loading to the apophysis or epiphysis. Most stress injuries of the knee resolve with relative rest but will occasionally need surgical intervention in more severe cases. Early and accurate identification is paramount for optimal management and to avoid long-term consequences.

Symptomatic Bipartite Patella in Adults Treated With Open Excision: Outcomes and Management.

Introduction Bipartite patella affects about 2% of people. Most cases are asymptomatic; however, some develop anterior knee pain during a sporting activity or trauma. When conservative treatment fails, surgery can be considered. This study aims to report the outcomes of fragment excision with or without lateral release in adults with the symptomatic bipartite patella. Methods The study was approved by the College of Medicine IRB. A retrospective review was performed. Patients were excluded if aged < 18 or had prior knee surgery. Data collected included: age, gender, BMI, sports played, occupation, physical exam findings, Saupe classification, conservative and surgical treatment, advanced imaging used, duration of follow-up, Lysholm score and postoperative complications. Results Eight patients were studied. The average age was 28.4 years and BMI was 31.5. Sporting activities included hunting, swimming, soccer, golfing and softball. Occupations included office job, laborer, manufacturing plant worker and truck driver. All patients complained of anterior knee pain exacerbated by sports or work. All patients failed >6 months of conservative treatment. Saupe classification included seven types III (superolateral) and one type II (lateral). Surgical treatment included one open excision, six arthroscopic-assisted open excisions and one arthroscopic-assisted open excision with the lateral release. The duration of follow-up averaged 15 months. The average preoperative and postoperative Lysholm score was 75 and 93, respectively. One postoperative complication occurred. Conclusions Bipartite patella is an uncommon cause of anterior knee pain in adults. When pain persists despite conservative care, fragment excision of less than 12% of the whole patella with or without lateral release resulted in excellent outcomes in the majority of cases.

Painful bipartite patella following injury: a case report.

Bipartite patella is a normal variation in ossification development. This variation is usually asymptomatic but can cause persistent and debilitating anterior knee pain with an injury. We report the case of a 56-year-old man complaining of persistent anterior left knee pain following trauma. Standard knee radiographs show a bilateral Bipartite Patella appearance, and magnetic resonance imaging shows discrete bony edema of the cancellous bone of the accessory bone and about the synchondrosis explaining the anterior knee pain, associated with a crack in the posterior compartment of the medial meniscus. Conservative care including medical treatment with non-steroidal anti-inflammatory drugs, physical therapy was used. Magnetic resonance imaging is the most valuable diagnostic tool for evaluating detailed morphologic and pathologic changes in patients with the bipartite patella.

Arthroscopic Management for Bipartite Patella: A Systematic Review.

BACKGROUND: Bipartite patella is a rare congenital condition that becomes painful following direct trauma or an overuse injury. If it remains painful despite nonoperative treatment, surgery may be warranted. The current gold standard is open fragment excision or lateral release; however, arthroscopic management is also possible. PURPOSE: To investigate the safety and efficacy of arthroscopic treatment of painful bipartite patella. STUDY DESIGN: Systematic review; Level of evidence, 4. METHODS: Using Medline and Embase, we systematically reviewed the literature as of March 8, 2020, using the subject headings "bipartite patella" and "arthroscopy" and related key terms. All levels of evidence involving human studies in English were included. Articles were excluded if only the abstract was published or the study was related to nonsurgical treatment or nonrelated diagnoses. Data related to journal/article information, demographic/clinical data, arthroscopic technique, length of follow-up, treatment outcomes, and complications were extracted. RESULTS: Eleven articles with 43 patients were included in the review. Most patients (n = 34; 79%) underwent arthroscopic lateral release, while 16% (n = 7) had arthroscopic excision of the accessory fragment and 5% (n = 2) had arthroscopic excision and release. All patients except for one, who experienced postoperative trauma, were pain-free after arthroscopic treatment and were able to return to sports after a mean 2.6 months. CONCLUSION: This review demonstrated that arthroscopic management of painful bipartite patella is a safe and effective alternative to open surgical excision or release. However, all articles were case studies or small case series, owing to the rarity of the condition. In the future, higher-level studies comparing arthroscopic techniques and postoperative rehabilitation programs should be performed.

Operative Treatment of Bipartite Patella in Pediatric and Adolescent Athletes: A Retrospective Comparison With a Nonoperatively Treated Cohort.

BACKGROUND: Bipartite patella (BPP) is a developmental anomaly that forms when incomplete patellar ossification leaves a residual fibrocartilaginous synchondrosis between ossification centers. Repetitive traction forces across the synchondrosis can cause knee pain, most commonly presenting in adolescence. Symptoms frequently resolve with nonoperative management. Few surgical case series exist to guide treatment approaches for refractory pain. PURPOSE: To investigate the clinical features, surgical techniques, and outcomes associated with operative treatment of symptomatic BPP in pediatric and adolescent athletes and to compare features of the series with a large control group managed nonoperatively. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: A retrospective medical record review was conducted of all patients aged ≤20 years who were diagnosed with symptomatic, radiologically confirmed BPP between 2003 and 2018 at a single tertiary-care pediatric hospital (N = 266). Demographic and clinical variables were analyzed, and additional radiologic and perioperative variables were collected for the surgical subcohort. RESULTS: Of the 266 patients included, 27 were treated operatively (10.2%). When compared with those treated nonoperatively (with rest, physical therapy, cryotherapy, and anti-inflammatory medications), the operatively managed group experienced a longer duration of symptoms before first presentation (21.5 vs 7.6 months; P < .001) and were more likely to be older (mean age, 15.4 vs 12.4 years; P < .001), female (59.3% vs 35.6%; P = .03), and competitive athletes (100% vs 84.5%; P = .02). In the 27 patients treated operatively, procedures were categorized as isolated fragment excision (n = 9), fragment excision with lateral release (n = 8), isolated lateral release (n = 5), fragment screw fixation (n = 4), and synchondrosis drilling (n = 1). The mean time between surgery and return to sports was 2.2 months. Four patients (14.8%) reported residual symptoms requiring secondary surgery, including lateral release (n = 1), excision of residual fragment (n = 1), and fixation screw removal (n = 2). CONCLUSION: BPP can cause knee pain in adolescent athletes and is generally responsive to nonoperative treatment. Patients undergoing surgical treatment-most commonly female competitive athletes with prolonged symptoms-represented 10% of cases. A variety of surgical techniques may be effective, with a 15% risk of persistent or recurrent symptoms warranting reoperation. Prospective multicenter investigations are needed to identify optimal candidates for earlier interventions and the optimal operative treatment technique.

Intra-osseous tophaceous gout of a bipartite patella mimicking aggressive bone tumour.

This is a very rare case of gouty tophus in the patella of a 31-year-old male, without any medical co-morbidities. The patient initially presented after an injury to left knee but came back months later due to persistence of pain. Surgical decision was made based on imaging findings in computed tomography and magnetic resonance imaging of an intraosseous lesion that has increased in size. The initial diagnosis is that of an aggressive bone tumour. The diagnosis of an intraosseous gout was made intra-operatively upon seeing the characteristics of the lesion, and upon confirmation of the biopsy results. Gout can usually be managed medically with urate lowering drugs and lifestyle change. However, when presented with a tophus that is increasing in size and causing mass effect on the involved bone, surgical management is indicated.

Ultrasound-guided injection and the pie crust technique for the treatment of symptomatic bipartite patella.

PURPOSE: This study aimed to investigate the results of a new treatment procedure (ultrasound-guided injection and the "pie crust" technique for lengthening of capsular tendon structures) for symptomatic bipartite patella. METHODS: We retrospectively investigated patient outcomes following the treatment of symptomatic type III bipartite patella with our new technique. Fifteen knees in 14 boys (mean age, 13.0 ± 1.7 years) were included. The procedure involved the injection of 1% lidocaine (2 mL) and triamcinolone acetonide (5 mg) between the patella and fragment. We then punctured 10 sites from one skin puncture to extend lateral capsular tendon structures. The patients were clinically assessed using the Victorian Institute of Sports Assessment (VISA) score before and 1 week, 1 month, and 3 months after the procedure. Patients were also evaluated for complications. RESULTS: The average VISA score was 45.7 ± 4.7 before treatment, 70.6 ± 7.3 at 1 week post-treatment, 84.4 ± 16.6 at 1 month post-treatment, and 88.6 ± 18.3 at 3 months post-treatment. The VISA score improvement from before the procedure to 1 week after the procedure was significant (P < 0.01). There were no complications in any of the patients, who returned to sports at a mean of 4.2 ± 2.1 weeks after the procedure. However, two patients (three knees) had poor results and could not return to action; thus, they underwent surgical treatment 4 months after the ultrasonographic procedure. CONCLUSIONS: This novel method is a potential treatment option for the management of symptomatic bipartite patella in outpatient clinics.

Synchondrosis Bither Block: A New Addition in the Diagnosis of Symptomatic Bipartite Patella.

Symptomatic bipartite patella is uncommon, and to ensure good outcome, patient selection is the key. Mostly assigning the pain origin to the nonfused fragment is easy though, in few cases, can be a serious dilemma, especially in the absence of direct tenderness over nonfused fragment. The decision of surgical intervention is solely made on the criteria of exclusion of other causes in the presence of persistent anterior knee pain. The literature focuses on different treatment techniques and outcomes with a rare attempt to add to the currently available supporting tests to affirmatively ascertain the cause-pain relation to the bipartite fragment. This article defines the synchondrosis block to assist the surgeon in isolating the source of pain to bipartite fragment in symptomatic knee.

Bipartite patella separation and partial quadriceps tendon rupture in the setting of trauma.

Normal development of the patella typically involves fusion of secondary ossification centers into a single bone during adolescence, with failure of fusion resulting in bipartite and tripartite patellae. In such variants, injury to incomplete ossification center fusion, though uncommon, has been reported to occur in the setting of traumatic quadriceps tendon rupture. The authors present a rare and complex case of traumatic bipartite fragment separation, patellar avulsion, and a complex partial quadriceps tendon tear confirmed surgically in a 36-year-old male. In this case, a tear in the lateral aspect of the quadriceps tendon attached to the nonfused patellar ossification center resulted in retraction of the band containing the bipartite fragment and separation of the patellar fragments, with superior displacement of the smaller bony avulsion likely due to complex attachments from the medial aspect of the quadriceps tendon. Knowledge of the classical locations of a bipartite and tripartite patella can aid in the differentiation of the anatomic variant versus patellar avulsion. Additionally, knowledge of the variable and complex nature of the quadriceps tendon aids in understanding the process of patellar avulsions and various tears, leading to the appropriate orthopedic management.

Osteonecrosis of bipartite patella following total knee arthroplasty without lateral release.

We present a case of osteonecrosis of bipartite patella occurring after total knee arthroplasty using medial parapatellar approach without lateral retinacular release in osteoarthritic knee of a 66 year-old-male. The surgery was performed using traditional technique with medial parapatellar approach and patella was resurfaced. Patella was everted during surgery. There was no event during follow-up period after surgery. Range of motion of the knee was 135° without flexion contracture. Eight months after the surgery, patella was fragmented and resorbed on the radiographs which was consistent with osteonecrosis. The patient showed extension limitation of 30° with no pain. Patellar osteonecrosis has been rarely reported after total knee arthroplasty with lateral retinacular release. However, there was no report of patellar osteonecrosis after total knee arthroplasty without lateral retinacular release. Caution should be taken about patellar osteonecrosis in case of bipartite patella even though lateral retinaculum is preserved during total knee arthroplasty.

Evaluation and management of knee pain in young athletes: overuse injuries of the knee.

Recurrent or chronic activity related knee pain is common in young athletes. Numerous intrinsic conditions affecting the knee can cause such pain. In addition, knee pain can be referred pain from low back, hip or pelvic pathology. The most common cause of knee pain in young athletes is patellofemoral pain syndrome, or more appropriately termed idiopathic anterior knee pain. Although, numerous anatomical and biomechanical factors have been postulated to contribute the knee pain in young athletes, the most common underlying reason is overuse injury. In this paper, we have reviewed selected conditions that case knee pain in athletes, including anterior knee pain syndrome, Osgood-Schlatter disease, Sinding-Larsen-Johanssen syndrome, juvenile osteochondritis dissecans (JOCD), bipartite patella, plica syndrome, and tendonitis around the knee.

Successful Treatment of Painful Synchondrosis of Bipartite Patella after Direct Trauma by Operative Fixation: A Series of Six Cases.

INTRODUCTION: The patella is the largest sesamoid bone in the body and may have one (77%) or multiple (23%) ossification centres. Patellar and patellofemoral joint abnormalities are a common cause of anterior knee pain but symptomatic bipartite patella is an uncommon problem. CASE SERIES: We report a series of six cases of painful synchondrosis in bipartite patellae, all in keen athletes following a direct blow to the anterior aspect of the knee. A complete rupture of the synchondrosis with evidence of retropatellar chondral separation was seen on MRI scan in all cases. Successful surgical fixation was undertaken with complete resolution of symptoms in all patients at an average of three months post-operatively. CONCLUSION: Painful synchondrosis of a bipartite patella in young and active individuals following direct trauma is a relatively rare cause of anterior knee pain, but may be associated with significant morbidity. In cases refractory to non-operative management, successful symptomatic treatment can be achieved by operative fixation.

Forensic Identification of Bipartite Patella Misdiagnosed as Patella Fracture.

Bipartite patella is recognized as a developmental anomaly of ossification. Most of them are asymptomatic and are discovered incidentally. Bipartite patella is sometimes misdiagnosed as a patella fracture, because the x-ray images of both these conditions may appear very similar. In this case, the patient complained of left knee pain after x-ray films revealed a fracture-like line in the left patella. The patient was then diagnosed as having a patella fracture. In China, the injury degree is categorized as serious injury, minor injury, and trivial injury. As the injury degree of patellar fracture is identified as minor injury, the defendant who injured the patient will be sentenced to prison for ≤3 years. However, the defendant objected to this judgment and applied for the second evaluation of injury degree. On the basis of the site of injury, clinical manifestations, and imaging findings, we diagnosed the patient with bipartite patella which belongs to normal anatomic variant. Therefore, the injury degree of the patient was not minor injury.

BIPARTITE PATELLA IN 35-YEAR-OLD FITNESS INSTRUCTOR: A CASE REPORT.

BACKGROUND AND PURPOSE: The patella plays an important role in knee biomechanics and provides anterior coverage of the knee joint. One to two percent of the population has an anatomical variant of patella called a bipartite patella that usually does not case pain. However, occasionally after injury or overuse during sport it can be a source of anterior knee pain. The purpose of this case report was to present a rare variant of bipartite patella and highlight conservative treatment of this condition. STUDY DESIGN: Case Report. CASE DESCRIPTION: A 35-year-old female patient presented with persistent bilateral non-traumatic anterior knee pain of a six-year duration that was enhanced by strenuous kinds of sport activity. Standard radiographs and MRI revealed the presence of bipartite patella with medial pole cartilage edema bilaterally. Conservative care including physical therapy, extracorporeal shock wave therapy (ESWT), and viscosupplementation was utilized. OUTCOME: After treatment VAS decreased to 0/10 from 5/10 in the left knee and 1/10 from 5/10 in the right knee. The Kujala Scores improved after treatment to 100 and 95 for the left and right knees respectively. The subject returned to full sport activity and work as a fitness instructor without pain and limitations. DISCUSSION: This case describes a rare finding of bilateral medial bipartite patella and the successful use of physical therapy with viscosupplementation in patellar pain caused by bipartite patella. It also supports the use of Extra Corporeal Shock Wave Therapy in bipartite patella pain as a supplement for therapy. LEVEL OF EVIDENCE: 4.

Unique patellofemoral alignment in a patient with a symptomatic bipartite patella.

BACKGROUND: A symptomatic bipartite patella is rarely seen in athletic adolescents or young adults in daily clinical practice. To date, only a limited number of studies have focused on patellofemoral alignment. The current study revealed a unique patellofemoral alignment in a patient with a symptomatic bipartite patella. METHODS: Twelve patients with 12 symptomatic bipartite patellae who underwent arthroscopic vastus lateralis release (VLR) were investigated (10 males and two females, age: 15.7±4.4years). The radiographic data of contralateral intact and affected knees were reviewed retrospectively. From the lateral- and skyline-view imaging, the following parameters were measured: the congruence angle (CA), the lateral patellofemoral angle (LPA), and the Caton-Deschamps index (CDI). As an additional parameter, the bipartite fragment angle (BFA) was evaluated against the main part of the patella in the skyline view. RESULTS: Compared with the contralateral side, the affected patellae were significantly medialized and laterally tilted (CA: P=0.019; LPA: P=0.016), although there was no significant difference in CDI (P=0.877). This patellar malalignment was found to significantly change after VLR (CA: P=0.001; LPA: P=0.003) and the patellar height was significantly lower than in the preoperative condition (P=0.016). In addition, the BFA significantly shifted to a higher degree after operation (P=0.001). CONCLUSIONS: Patients with symptomatic bipartite patellae presented significantly medialized and laterally tilted patellae compared with the contralateral intact side. This malalignment was corrected by VLR, and the alignment of the bipartite fragment was also significantly changed. LEVEL OF EVIDENCE: Level IV, case series.

Prevalence of bipartite patella in Turkish population: analysis of bilateral knee radiographs in 897 subjects / Prevalencia de patela bipartita en una población turca: análisis de radiografías bilaterales de rodilla en 897 sujetos

Bipartite patella is a normal anatomic variant of patella. There are various data about the prevalence of bipartite patella in the literature. The aim of this study was to investigate its prevalence, type distribution and sex predilection in Turkish population. Bilateral knee radiographs were retrospectively reviewed of 897 consecutive adult patients. Cases with bipartite patella were categorized according to the Oohashi classification. Medical records were examined in order to differentiate symptomatic and asymptomatic bipartite patellae. We contacted symptomatic patients by telephone to learn continuity of knee pain. We identified 11 cases (7 male, 4 female) of bipartite patella among the 283 male and 614 female patients. No bilateral cases were identified. The prevalence of bipartite patella was 1.22% overall, 2.47% in males, and 0.65% in females. The most common type was superolateral bipartite patella as seen in 9 patients (81.8%). One subject had lateral bipartite and one subject had superolateral tripartite patella. Painful bipartite patella was found in only 2 patients (18%). One of them had continuing symptoms even after 12 months. In conclusion, we found that the prevalence of bipartite patella in Turkish population was approximately 1%. Both inclusion of only adult (skeletally mature) subjects and assessment with bilateral imaging increased the reliability of this value. In accordance with the literature, bipartite patella was found significantly more frequent in males and mostly in superolateral type. More studies are needed in order to obtain the prevalence, type and sex distribution of bipartite patella in different populations.

La patela bipartita es una variante anatómica normal. En la literaturahay varios datos sobre la prevalencia de patela bipartitae. El objetivo de este estudio fue investigar la prevalencia, distribución y aparición según sexo en la población turca. Se revisaron retrospectivamente radiografías bilaterales de rodilla de 897 pacientes adultos. Los casos con patela bipartita se clasificaron de acuerdo a la clasificación de Oohashi. Fueron examinados los registros médicos de los pacientes con el fin de diferenciar los casos de patela bipartita sintomática y asintomática. Se estableció contacto con los casos sintomáticos por teléfono para conocer la continuidad del dolor de rodilla. Se identificaron 11 casos (7 varones, 4 mujeres) de patela bipartita entre 283 hombres y 614 pacientes de sexo femenino. No se identificaron casos bilaterales. La prevalencia de patela bipartita fue de 1,22% en total, 2,47% en varones y 0,65% en las mujeres. El tipo más común fue la patela bipartita superolateral en 9 pacientes (81,8%). Un sujeto presentó patela bipartita lateral y en otro caso, patela tripartita superolateral. La patela bipartita dolorosa fue encontrada en sólo 2 pacientes (18%). Uno de ellos presentó síntomas que continuaron incluso después de 12 meses. En conclusión, se encontró que la prevalencia de la patela bipartita en la población turca fue de aproximadamente un 1%. La inclusión en esta investigación de solo sujetos adultos (con el esqueleto maduro) y el estudio de imágenes bilaterales aumentó la fiabilidad de estos parámetros. De acuerdo con la literatura, la patela bipartita se encontró significativamente de manera más frecuente en hombres y en su mayoría se trató del tipo superolateral. Se necesitan más estudios para obtener la prevalencia, tipo y distribución por sexo de la patela bipartita en diferentes poblaciones.

Return to activity among athletes with a symptomatic bipartite patella: a systematic review.

BACKGROUND: A bipartite patella is typically rare, but can become symptomatic during overuse activities such as those performed during athletic events. Therefore, this anomaly typically presents in the young, athletic population, often inhibiting athletic activities. Multiple treatment options exist, with nonsurgical management frequently adopted as the initial treatment of choice. PURPOSE: To determine the most effective intervention in returning athletes with symptomatic bipartite patella to their prior activity levels. METHODS: A systematic review of the literature was performed using PRISMA guidelines to identify studies reporting outcomes of athletes' ability to return to activity following treatment for a symptomatic bipartite patella. The type of intervention, type of bipartite classification, outcomes, and complications were recorded. RESULTS: Twenty articles with a total of 125 patients and 130 knees were identified and included in this review. A total of 105 athletes made a full return to athletic activity following treatment for their painful bipartite patella. One hundred athletes (85.5%) that underwent surgical treatment were able to make a full return to their sport without symptoms, although this varied by surgical procedure performed. Excision of the painful fragment produced the best results in returning athletes to sport, with 91% returning without symptoms and nine percent returning but with residual symptoms. CONCLUSION: Surgical treatments for symptomatic bipartite patellae are successful at returning athletes to their same level of play, and best outcomes are with excision of the fragment. These results are limited, however, due to the poor quality of original data given the rarity of the anomaly and the underrepresented conservative treatment group.