Computed diffusion-weighted imaging with a low-apparent diffusion coefficient-pixel cut-off technique for breast cancer detection.

OBJECTIVE: This study aimed to compare the image quality and diagnostic performance of computed diffusion-weighted imaging (DWI) with low-apparent diffusion coefficient (ADC)-pixel cut-off technique (cDWI cut-off) and actual measured DWI (mDWI). METHODS: Eighty-seven consecutive patients with malignant breast lesions and 72 with negative breast lesions who underwent breast MRI were retrospectively evaluated. Computed DWI with high b-values of 800, 1200, and 1500 s/mm2 and ADC cut-off thresholds of none, 0, 0.3, and 0.6 (×10-3 mm2/s) were generated from DWI with two b-values (0 and 800 s/mm2). To identify the optimal conditions, two radiologists evaluated the fat suppression and lesion reduction failure using a cut-off technique. The contrast between breast cancer and glandular tissue was evaluated using region of interest analysis. Three other board-certified radiologists independently assessed the optimised cDWI cut-off and mDWI data sets. Diagnostic performance was evaluated using receiver operating characteristic (ROC) analysis. RESULTS: When an ADC cut-off threshold of 0.3 or 0.6 (× 10-3 mm2/s) was applied, fat suppression improved significantly (p < .05). The contrast of the cDWI cut-off with a b-value of 1200 or 1500 s/mm2 was better than the mDWI (p < .01). The ROC area under the curve for breast cancer detection was 0.837 for the mDWI and 0.909 for the cDWI cut-off (p < .01). CONCLUSION: The cDWI cut-off provided better diagnostic performance than mDWI for breast cancer detection. ADVANCES IN KNOWLEDGE: Using the low-ADC-pixel cut-off technique, computed DWI can improve diagnostic performance by increasing contrast and eliminating un-suppressed fat signals.

Impact of pain in other body regions on the foot-specific quality of life in patients with hallux valgus.

OBJECTIVES: The purpose of this study was to clarify the prevalence of pain outside the foot, and to determine the associations of pain outside the foot with foot-specific quality of life (QOL) in patients with hallux valgus. METHODS: Patients scheduled to undergo hallux valgus surgery were recruited. Patients answered whether they experienced disabling pain in 13 body regions other than the foot. Foot-specific QOLwas assessed using the Self-Administered Foot Evaluation questionnaire (SAFE-Q). Foot pain was quantified using the visual analogue scale (VAS). Patient characteristics, including age, sex, comorbidity, anxiety, and depression, were also surveyed. The association between pain elsewhere and the SAFE-Q and pain VAS scores were assessed using univariate and multivariate analyses. RESULTS: Of 102 patients, 55 (54%) experienced pain other than the foot. All SAFE-Q subscale scores were lower, and pain VAS was higher in patients with pain elsewhere than in patients without. In the multivariate analysis, an increase in the number of pain regions was independently associated with a decrease in SAFE-Q scores and an increase in pain VAS. CONCLUSION: More than half of the patients with hallux valgus experienced pain elsewhere. The presence of pain elsewhere was associated with poorer foot-specific QOL and severer foot pain.

Detecting lymph node metastasis of esophageal cancer on dual-energy computed tomography.

BACKGROUND: Using conventional computed tomography (CT), the accurate diagnosis of lymph node (LN) metastasis of esophageal cancer is difficult. PURPOSE: To examine dual-energy CT parameters to predict LN metastasis preoperatively in patients with esophageal cancer. MATERIAL AND METHODS: Twenty-six consecutive patients who underwent dual-energy CT before an esophageal cancer surgery (19 patients with LN metastases) were analyzed. The included LNs had a short-axis diameter of ≥4 mm and were confirmed to be resected on postoperative CT. Their short-axis diameter, CT value, iodine concentration (IC), and fat fraction were measured on early- and late-phase contrast-enhanced dual-energy CT images and compared between pathologically confirmed metastatic and non-metastatic LNs. RESULTS: In total, 51 LNs (34 metastatic and 17 non-metastatic) were included. In the early phase, IC and fat fraction were significantly lower in the metastatic than in the non-metastatic LNs (IC = 1.6 mg/mL vs. 2.2 mg/mL; fat fraction = 20.3% vs. 32.5%; both P < 0.05). Furthermore, in the late phase, IC and fat fraction were significantly lower in the metastatic than in the non-metastatic LNs (IC = 2.0 mg/mL vs. 3.0 mg/mL; fat fraction = 20.4% vs. 33.0%; both P < 0.05). Fat fraction exhibited accuracies of 82.4% and 78.4% on early- and late-phase images, respectively. Conversely, short-axis diameter and CT value on both early- and late-phase images were not significantly different between the metastatic and non-metastatic LNs (P > 0.05). CONCLUSION: Using dual-energy CT images, IC and fat fraction are useful for diagnosing LN metastasis in patients with esophageal cancer.

Egg-Cracking Vibration as a Cue for Stink Bug Siblings to Synchronize Hatching.

Egg clutches of many animals hatch synchronously due to parental control [1, 2] or environmental stimulation [3, 4]. In contrast, in some animals, embryos actively synchronize their hatching timing with their siblings to facilitate adaptive behavior in sibling groups, such as mass migration [5, 6]. These embryos require synchronization cues that are detectable from eggs and indicative of when the siblings hatch, such as pre-hatching vocalizations in birds and crocodiles [7, 8]. Previous studies, using methods including artificial presentation of non-specific mechanical stimuli, demonstrated that vibrations or other mechanical forces caused by sibling movements are cues used by some turtles and insects [9-13]. However, there is no evidence about which movements of tiny embryos or hatchlings, among multiple possibilities, can generate mechanical cues actually detectable through eggs. Here, we show that embryos of the brown marmorated stink bug, Halyomorpha halys, synchronize hatching by responding to single pulsed vibrations generated when siblings crack open their eggshells. An egg-cracking vibration seems to be transmitted to distant eggs within a clutch while still maintaining its function as a cue, thus leading to the highly synchronized hatching pattern previously reported [14]. In this species, it is possible that embryos attempt to hatch with short lags after earlier-hatched siblings to avoid egg cannibalism by them [14]. The present study illustrates the diversity of social-information use by animal embryos for success in the sibling group.

Age-dependent differences in response to partial-thickness cartilage defects in a rat model as a measure to evaluate the efficacy of interventions for cartilage repair.

The objectives of this study are (1) to examine age-dependent longitudinal differences in histological responses after creation of partial-thickness articular cartilage defects (PTCDs) in rats and to use this model (2) to objectively evaluate the effectiveness of interventions for cartilage repair. Linear PTCDs were created at a depth of 100 µm in the weight-bearing region of the medial femoral condyle in rats of different ages (3 weeks, 6 weeks, 10 weeks and 14 weeks). One day, one week, two weeks, four weeks and twelve weeks after PTCD generation, spontaneous healing was evaluated histologically and immunohistochemically. Effects of interventions comprising mesenchymal stem cells (MSCs) or platelet-rich plasma (PRP) or both on 14-week-old PTCD rats were evaluated and compared with natural courses in rats of other ages. Younger rats exhibited better cartilage repair. Cartilage in 3-week-old and 6-week-old rats exhibited nearly normal restoration after 4-12 weeks. Cartilage in 14-week-old rats deteriorated over time and early signs of cartilage degeneration were observed. With injection of MCSs alone or MSCs + PRP, 14-week-old PTCD rats showed almost the same reparative cartilage as 6-week-old rats. With injection of PRP, 14-week-old PTCD rats showed almost the same reparative cartilage as 10-week-old rats. This model will be of great use to objectively compare the effects of interventions for small cartilage lesions and may help to advance the development of disease-modifying osteoarthritis drugs.

Comparative Analysis of Gene Expression between Cartilage and Menisci in Early-Phase Osteoarthritis of the Knee-An Animal Model Study.

Cartilage degeneration is believed to be the primary event in the development of osteoarthritis (OA). On the other hand, meniscal degeneration is observed with high prevalence, and some researchers have pointed out that pathological changes in menisci precede that of cartilage. The purpose of the present study is to investigate comprehensive gene expression pattern of cartilage and menisci in the initial phase of surgically induced OA and to compare them. Secondary OA was surgically induced in 10-week-old male Wistar rats by anterior cruciate ligament transection (ACLT). Articular cartilage and menisci were separately dissected from six ACLT- and six sham-operated rats. Each specimen was analyzed by microarray, histological, and immunohistochemical analysis 3 weeks after surgery. Of the 36,685 transcripts detectable by microarray, the number of upregulated transcripts in ACLT menisci was >2.5-fold compared with that in ACLT menisci in any given threshold. Cluster analysis using the Database for Annotation Visualization and Integrated Discovery (DAVID) showed genes related to OA, such as response to stimulus, angiogenesis, and apoptosis, which were predominantly found in menisci in ACLT rats. Representative proteases including Adamts2, 4, Mmp2, 12, 13, 14, 16, extracellular matrix genes including versican (Vcan), lumican (Lum), syndecan1 (Sdc1), and Prostaglandin endoperoxide synthase2 (Ptgs2) were up-regulated in menisci, but were not up-regulated in cartilage. Our results indicated that the molecular changes that occurred in menisci preceded those occurred in cartilage in the very early phase of surgically induced OA models.

Treatment of Atypical Ulnar Fractures Associated with Long-Term Bisphosphonate Therapy for Osteoporosis: Autogenous Bone Graft with Internal Fixation.

Long-term bisphosphonate use has been suggested to result in decreased bone remodelling and an increased risk of atypical fractures. Fractures of this nature commonly occur in the femur, and relatively few reports exist to show that they occur in other bones. Among eight previous reports of atypical ulnar fractures associated with bisphosphonate use, one report described nonunion in a patient who was treated with cast immobilization and another described ulna nonunion in one of three patients, all of whom were treated surgically with a locking plate. The remaining two surgical patients achieved bone union uneventfully following resection of the osteosclerotic lesion and iliac bone grafting before rigid fixation. We hypothesized that the discontinuation of bisphosphonate therapy, the use of teriparatide treatment, and low-intensity pulsed ultrasound (LIPUS) might have been associated with fracture healing.

Balloon-occluded retrograde transvenous obliteration using a new microballoon for gastric varices.

We here present a case involving a complicated type of gastric fundal varices treated by balloon-occluded retrograde transvenous obliteration. A newly developed 1.8-Fr tip coaxial microballoon catheter was successfully advanced into narrow and tortuous varices, and a sclerosant could be infused in a reasonable manner, avoiding reflux into collaterals. Divided injections of sclerosant were performed over two days, via a microballoon catheter that remained inserted overnight with balloon inflation, and the sclerosant could be infused sufficiently in the entirety of the varices. The varices were completely thrombosed and prominently reduced.

Changes in the syndesmotic reduction after syndesmotic screw fixation for ankle malleolar fractures: One-year longitudinal evaluations using computer tomography.

INTRODUCTION: To evaluate time-dependent changes in the syndesmotic reduction after syndesmotic screw fixation and one year after screw removal for ankle malleolar fractures, and to assess whether the incidence of syndesmotic malreduction changes depending on the measurement method. METHODS: We assessed twenty patients who underwent syndesmotic screw fixation for ankle fractures. The syndesmotic screws were removed after six weeks of the fracture surgery. Syndesmotic reduction was assessed within two weeks of the fracture surgery and one year after the screw removal using the axial computer tomographic images. Side-to-side differences in the anterior and posterior tibiofibular distances, anteroposterior fibular translation, and fibular rotation were measured. RESULTS: The mean anterior tibiofibular distance was 0.7mm after syndesmotic fixation. It increased to 1.9mm at one year after screw removal (p=0.002). After syndesmotic fixation, four ankles had malreduction of the anterior tibiofibular distance, including three ankles with widening and one with overtightening. At one year, eight ankles had malreduction, all of whom had widening. The other measurement values did not change over time (0.1mm vs. 0.6mm for the posterior tibiofibular distance, 0.2mm vs. 0.3mm for the anteroposterior fibular translation, and 0.7° vs. 0° for the fibular rotation). The incidences of malreduction were significantly different depending on the definition of malreduction, ranging from 10% to 50% after syndesmotic fixation (p=0.01) and from 20% to 60% at one year after screw removal (p=0.02). CONCLUSIONS: The anterior tibiofibular distance widened after one year of syndesmotic screw removal. The incidence of malreduction varied depending on the measurement method.

Quality of Life in Patients With Untreated and Symptomatic Hallux Valgus.

BACKGROUND: The purposes of this study were to compare the quality of life (QOL) of subjects who had untreated symptomatic hallux valgus with the QOL of the general population and to investigate factors associated with the QOL of the subjects. METHODS: One hundred sixteen subjects with previously untreated and symptomatic hallux valgus were surveyed. QOL was assessed using the 36-item Short Form Health Survey (SF-36). Additionally, clinical evaluations (the visual analog scale for pain, Japanese Society for Surgery of the Foot Scale, lesser toe pain, and pain in other parts of the body) and radiographic evaluations (hallux valgus angle, intermetatarsal angle between the first and second metatarsals, and dislocation of the second metatarsophalangeal joint) were performed. Differences in the SF-36 between the subjects and the general population were tested using independent t tests. Correlations between the QOL measurements, clinical evaluations, and radiographic evaluations were assessed using Spearman rank correlation coefficient. RESULTS: All SF-36 subscales and physical component summary scores for the subjects were significantly lower than those of the general population. Notably, the standardized physical function subscale (38.2 ± 15.8, P < .001) and physical component summary scores (38.9 ± 14.5, P < .001) were more than 10 points lower than those of the general population. Most QOL and clinical evaluation parameters were not correlated or were negligibly correlated with radiographic evaluations. Similarly, lesser toe pain or pain in other parts of the body was not correlated with QOL or clinical evaluations. CONCLUSION: The QOL of untreated and symptomatic hallux valgus subjects was lower than that of the general population. All QOL and clinical evaluation parameters were not significantly or negligibly correlated with the severity of toe deformities. Surgical decision making should not be based on the severity of the deformity alone, but rather patient QOL should also be carefully assessed. LEVEL OF EVIDENCE: Level III, comparative series.

Balloon-occluded arterial stump pressure before balloon-occluded transarterial chemoembolization.

OBJECTIVE: To evaluate balloon-occluded arterial stump pressure (BOASP), which is responsible for effective balloon-occluded transarterial chemoembolization (B-TACE), at each hepatic arterial level before B-TACE using a 1.8-French tip microballoon catheter for unresectable hepatocellular carcinoma (HCC). MATERIAL AND METHODS: The BOASP at various embolization portions was retrospectively investigated. "Selective" and "non-targeted" BOASP was defined as the BOASP at the subsegmental or segmental artery and the lobar artery, respectively. RESULTS: The measurement of the BOASP was carried out in 87 arteries in 47 patients. BOASP > 64 mmHg was revealed in the caudate lobe artery (A1) and the left medial segmental (A4), right anterior superior segmental (A8), anterior segmental, right and left hepatic arteries. Significant difference was noted in the incidence of BOASP above 64 mmHg between "non-targeted" and "selective" BOASP (p = 0.01). "Non-targeted" BOASP was significantly greater than "selective" BOASP (p = 0.0147). In addition, the BOASP in A1, 4, 8 and the anterior segmental arteries were significantly greater than in the other subsegmental and segmental arteries (p = 0.0007). CONCLUSION: "Non-targeted" B-TACE should be avoided to perform effective B-TACE and "selective" B-TACE at A1, 4, 8 and the anterior segmental arteries may become less effective than at the other segmental or subsegmental arteries.

Tendoscopic Excision of an Intratendinous Ganglion in the Flexor Hallucis Longus Tendon: A Case Report.

Intratendinous ganglion cysts are rare lesions of unknown etiology that originate within a tendon. We report the case of a 34-year-old female with an intratendinous ganglion in the plantar portion of the flexor hallucis longus tendon. The intratendinous ganglion recurred after ultrasound-guided needle aspiration. Tendoscopic excision of the intratendinous ganglion cyst achieved a satisfactorily result without recurrence.

Shape of the lateral edge of the first metatarsal head changes depending on the rotation and inclination of the first metatarsal: a study using digitally reconstructed radiographs.

BACKGROUND: Correction of pronation deformity and metatarsal primus varus is an important component of hallux valgus surgery, necessary to achieve a satisfactory correction and to prevent post-operative recurrence. Roundness of the lateral edge of the first metatarsal head (round sign) on the dorsoplantar radiograph of the foot has been empirically advocated as an indicator of first metatarsal pronation. The purpose of this study was to clarify the effect of rotation and inclination of the first metatarsal on the shape of the lateral edge of the first metatarsal head. METHODS: Computed tomographic images of feet in 30 subjects, without pathology of the first metatarsophalangeal joint, were included. Digitally reconstructed radiographs of the first metatarsal were created using the computed tomographic data. Thirty-nine images were created of each first metatarsal at different degrees of rotation (-10° to 30° of pronation) and inclination (-10° to 20° of plantarflexion). Then, the shape of the lateral edge of the first metatarsal head was classified into three types: angular, intermediate, and round. Generalized estimation equations were used to test if the shapes of the first metatarsal head were significantly different across the range of pronation and plantarflexion angles. RESULTS: The positive round sign changed to negative as the first metatarsal supinated. In most feet, these changes occurred as the pronation angle decreased from 10° to 0°. The positive round sign also changed to negative as the first metatarsal head plantarflexed. CONCLUSION: Positive round sign of the first metatarsal head on the dorsoplantar radiograph of the foot was significantly associated with increased pronation as well as decreased inclination of the first metatarsal. Negative round sign may be used as an indicator of effective correction of first metatarsal pronation during hallux valgus surgery.

Accuracy of high-resolution ultrasound in the detection of meniscal tears and determination of the visible area of menisci.

BACKGROUND: Imaging is of great importance in diagnosing meniscal tears. The aim of this study was to assess the accuracy of high-resolution ultrasound in the diagnosis of meniscal tears, with arthroscopic examination as the standard reference, after resolution was confirmed with a target-mounted reference phantom. An additional goal was to elucidate the area of the meniscus that could be visualized with the same ultrasound machine after placement of markers into the menisci of cadaveric knees. METHODS: Seventy patients were included for the assessment of the accuracy of a high-resolution ultrasound machine with a 14.0 to 6.0-MHz linear transducer. The preoperative ultrasound diagnosis, in terms of the presence and type of tear, was compared with that in the surgical reports. In the cadaveric studies, nine needles were placed in the peripheral zone of the menisci at regular intervals and the number of needles that could be observed with the system was recorded. RESULTS: The overall sensitivity, specificity, positive predictive value, and negative predictive value of ultrasound examination for meniscal tears were 88%, 85%, 85%, and 88%, respectively. These statistical parameters did not differ significantly between the medial and lateral menisci. The sensitivity for diagnosing horizontal, vertical, radial, flap, bucket-handle, and complex tears and for detecting discoid lateral menisci was 83%, 64%, 0%, 64%, 54%, 90%, and 80%, respectively. Ten percent of the lateral menisci could not be evaluated because of poor images. The cadaveric studies revealed that the ultrasound visualized the entire meniscus except for the anterior horn. CONCLUSIONS: The findings of this study suggest that ultrasound examination may be suitable for screening for meniscal tears. The fact that almost 10% of the lateral menisci could not be evaluated because of poor images appears to be a weakness of ultrasound.

Quantitative Assessment of Tendon Healing by Using MR T2 Mapping in a Rabbit Achilles Tendon Transection Model Treated with Platelet-rich Plasma.

PURPOSE: To determine if magnetic resonance (MR) imaging T2 mapping can be used to quantify histologic tendon healing by using a rabbit Achilles tendon transection model treated with platelet-rich plasma (PRP). MATERIALS AND METHODS: Experiments were approved by the Institutional Animal Care and Use Committee. The Achilles tendons of 24 New Zealand white rabbits (48 limbs) were surgically transected, and PRP (in the test group) or saline (in the control group) was injected into the transection site. The rabbits were sacrificed 2, 4, 8, and 12 weeks after surgery. Thereafter, T2 mapping and histologic evaluations were performed by using the Bonar scale. A mixed-model multivariate analysis of variance was used to test the effects of time and PRP treatment on the T2 value and Bonar grade, respectively. The correlation between the T2 value and Bonar grade was also assessed by using the Spearman correlation coefficient. RESULTS: The Bonar scale values decreased in both groups during tendon healing. The T2 value also shortened over time (P < .001 for both groups). The T2 values were positively correlated with the Bonar grade (ρ = 0.78, P < .001). Both the T2 value and Bonar scale value were lower in the PRP group than in the control group at 4, 8, and 12 weeks; however, there was no significant effect of PRP treatment on the T2 value or Bonar grade. CONCLUSION: The T2 value changes reflected histologic tendon healing. While T2 and Bonar grade were lower at all time points in tendons treated with PRP, there was no significant difference between the treatment and control tendons.

Transnodal lymphangiography and post-CT for protein-losing enteropathy in Noonan syndrome.

Noonan syndrome, which is a multiple congenital disorder, may be associated with lymphatic abnormalities. Protein-losing enteropathy (PLE) developing in Noonan syndrome is rare. We performed transnodal lymphangiography by directly accessing bilateral inguinal nodes under ultrasound guidance in a 17-year-old female with PLE developing in Noonan syndrome to assess detailed anatomical findings regarding lymphatic vessels. There have been no reports on transnodal lymphangiography for Noonan syndrome. Post-lymphangiographic CT images revealed multiple lymphatic abnormalities and lipiodol extravasation into the duodenum and the proximal jejunum. Transnodal lymphangiography was easy and safe for PLE developing in Noonan syndrome, and post-lymphangiographic CT provided invaluable information.

Manually controlled targeted prostate biopsy with real-time fusion imaging of multiparametric magnetic resonance imaging and transrectal ultrasound: an early experience.

OBJECTIVES: To report our early experience with manually controlled targeted biopsy with real-time multiparametric magnetic resonance imaging and transrectal ultrasound fusion images for the diagnosis of prostate cancer. METHODS: A total of 20 consecutive patients suspicious of prostate cancer at the multiparametric magnetic resonance imaging scan were recruited prospectively. Targeted biopsies were carried out for each cancer-suspicious lesion, and 12 systematic biopsies using the BioJet system. Pathological findings of targeted and systematic biopsies were analyzed. RESULTS: The median age of the patients was 70 years (range 52-83 years). The median preoperative prostate-specific antigen value was 7.4 ng/mL (range 3.54-19.9 ng/mL). Median preoperative prostate volume was 38 mL (range 24-68 mL). The number of cancer-detected cases was 14 (70%). The median Gleason score was 6.5 (range 6-8). Cancer-detected rates of the systematic and targeted biopsy cores were 6.7 and 31.8%, respectively (P < 0.0001). In six patients who underwent radical prostatectomy, the geographic locations and pathological grades of clinically significant cancers and index lesions corresponded to the pathological results of the targeted biopsies. CONCLUSION: Prostate cancers detected by targeted biopsies with manually controlled targeted biopsy using real-time multiparametric magnetic resonance imaging and transrectal ultrasound fusion imaging have significantly higher grades and longer length compared with those detected by systematic biopsies. Further studies and comparison with the pathological findings of whole-gland specimens have the potential to determine the role of this biopsy methodology in patients selected for focal therapy and those under active surveillance.

Balloon-occluded transarterial chemoembolization using a 1.8-French tip coaxial microballoon catheter for hepatocellular carcinoma: technical and safety considerations.

OBJECTIVE: To evaluate the technical feasibility and safety considerations of balloon-occluded transarterial chemoembolization (B-TACE) using a newly developed 1.8-French (Fr) tip microballoon catheter for hepatocellular carcinoma (HCC). MATERIAL AND METHODS: Between February 2013 and May 2013, 31 patients (20 males, 11 females; age range 56-85 years) underwent B-TACE using a 1.8-Fr tip microballoon catheter for unresectable HCC. The technical success rate, procedural complications, and adverse events of B-TACE were retrospectively investigated. RESULTS: A total of 31 patients were subjected to 70 sessions of B-TACE using a 1.8-Fr tip microballoon catheter. The level of B-TACE was sub-subsegmental in 11, subsegmental in 35, segmental in 14, lobar in five, and right inferior phrenic artery in five sessions. The overall technical success rate was 99% (69 out of 70 sessions). As procedural complications, rupturing of the microballoon (n = 3) and aneurysmal dilatation at the site of balloon occlusion (n = 2) were encountered. There were no significant differences in any parameters between blood biochemical examination before and between two to four weeks after the procedure. CONCLUSION: A 1.8-Fr tip microballoon catheter enables selective catheterization in patients with HCC and B-TACE using the 1.8-Fr tip microballoon catheter is a safe procedure.

Spontaneous repair of partial thickness linear cartilage injuries in immature rats.

Partial thickness articular cartilage injuries (PTCIs) were not previously thought to heal spontaneously. Immature rats have the capacity for spontaneous repair of PTCIs, although it is a long-term process. Our aim has been to examine the spontaneous repair response mechanism in immature rats. Single linear PTCIs were created in 3-week-old and 12-week-old rats in the direction of joint motion. On day 1 and at 1, 2, and 4 weeks after PTCI, evaluations of histological changes and immunohistology at the injury site and in the surrounding cartilage were performed. Anti-CD105 and anti-CD166 antibodies (as stem cell markers to identify mesenchymal stem cells in reparative cartilage tissue) were used for immunohistological evaluations. To determine whether endogenous repair ability existed in articular cartilage, an ex vivo experiment was also carried out. Femoral condyles with PTCIs were incubated in Dulbecco's modified Eagle's medium containing 10% fetal bovine serum for 1 day and for 1 and 2 weeks. Histological changes were subsequently examined. Immature cartilage showed a higher repair response than did mature cartilage, and the response occurred immediately after PTCI. In immature rats, CD105- and CD166-positive cells were found in the superficial and transitional zones of the articular cartilage. Few CD166-positive cells were identified in mature articular cartilage. No significant in vivo differences in the spontaneous repair responses to PTCIs were observed between mature and immature groups. Thus, the repair response to PTCIs seems to be associated not only with CD105- and CD166-positive cells, but also with other perichondral factors.