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.

The use of tourniquet is useful in terms of blood loss and soft tissue damage in arthroscopic anterior cruciate ligament reconstruction: a retrospective study.

Whether a tourniquet should be used for anterior cruciate ligament reconstruction (ACLR) when the operative field is secured remains controversial. Little is known about the influence of not using a tourniquet on total perioperative blood loss and soft tissue damage. The aim of this study was to compare total perioperative blood loss and soft tissue damage with and without tourniquet use during ACLR. Seventy-seven consecutive ACLRs in 76 patients were performed without tourniquet use at our hospital and enrolled in this study (T- group) between November 2018 and September 2021. The control group (T + group) comprised 55 historical ACLRs in 55 patients performed with tourniquet use at our hospital between April 2017 and September 2018. Total perioperative blood loss, calculated from the change in hemoglobin between that preoperatively and on postoperative day (POD) 1, and indicators of soft tissue damage including serum white blood cell (WBC) counts, creatine phosphokinase (CPK), and C-reactive protein (CRP) values measured on POD 1 and POD 7 were compared between groups. Total blood loss was significantly higher in the T- group (339 ± 216 mL) than in the T + group (258 ± 199 mL; P = 0.030). On POD 1, WBC counts were significantly higher in the T- group (9.7 ± 2.4 × 103 cells/µL) than in the T + group (9.1 ± 2.5 × 103 cells/µL; P = 0.043), CPK levels were significantly higher in the T- group (294 ± 417 U/L) than in the T + group (255 ± 88 U/L; P = 0.046), and CRP levels were also significantly higher in the T- group (1.40 ± 1.12 mg/dL) than in the T + group (0.91 ± 0.76 mg/dL; P = 0.016). No significant differences in WBC counts or CPK or CRP levels were seen between groups on POD 7. Total blood loss and soft tissue damage were significantly increased without tourniquet use during ACLR. No advantage was found for not using a tourniquet in terms of blood loss or soft tissue damage.

Simultaneous bilateral quadriceps tendon rupture in a healthy young male: a case report.

BACKGROUND: Simultaneous bilateral quadriceps tendon rupture is rare, particularly in young individuals with no prior medical history. We present the case of a young man who presented with bilateral quadriceps tendon rupture. CASE PRESENTATION: A 27-year-old Japanese man missed a step while descending a flight of stairs, stumbled, and became aware of severe pain in both knees. He had no past medical history, but was severely obese, with a body mass index of 43.7 kg/m2 (height 177 cm, weight 137 kg). Five days after injury, he was referred to our hospital for examination and treatment. Bilateral quadriceps tendon rupture was diagnosed based on magnetic resonance imaging, and quadriceps tendon repair with suture anchor was performed on both knees 14 days after injury. The postoperative rehabilitation protocol was to immobilize both knees in extension for 2 weeks, then to gradually proceed with weight-bearing and gait training using hinged knee braces. Both knees obtained a range of motion from 0° to 130° without any extension lag by 3 months postoperatively. One year postoperatively, tenderness was evident at the suture anchor in the right knee. That suture anchor was therefore removed in a second operation, and histological evaluation of the tendon of the right knee revealed no pathological changes. As of 19 months after the primary surgery, the patient showed a range of motion from 0° to 140° in both knees, did not complain of any disability, and had fully returned to normal daily activities. CONCLUSIONS: We experienced simultaneous bilateral quadriceps tendon rupture in a 27-year-old man with no past medical history other than obesity. Suture anchor repair was performed for both quadriceps tendon ruptures and achieved a favorable postoperative outcome.

Lateral Patellar Facetectomy Reduces the Incidence of Anterior Knee Pain in Patellar Resurfaced Total Knee Arthroplasty.

Lateral patellar facet impingement (LPFI) can cause anterior knee pain (AKP) after patellar resurfaced total knee arthroplasty (TKA). Recently, lateral patellar facetectomy (LPF), which has been used for LPFI, has been performed during primary TKA, providing good clinical outcomes. However, the effect of LPF on AKP in primary patellar resurfaced TKA has not been sufficiently studied. The purpose of this study was to examine the effect of LPF on the development of AKP in patellar resurfaced TKAs with minimum follow-up of 3 years. This retrospective cohort study included 84 knees of 66 consecutive patients who underwent patellar resurfaced TKA between April 2007 and November 2014 in our hospital. The subjects were divided into two groups: TKA with LPF (LPF group; 47 knees) and TKA without LPF (no-LPF group; 37 knees). Postoperative AKP, the primary outcome, the Japanese Orthopaedic Association (JOA) score, and range of motion were investigated at the final visit and compared between the two groups. Six knees (16.2%) had AKP in the no-LPF group, whereas none of the knees had AKP in the LPF group at the final visit. The incidence of AKP was significantly lower in the LPF group (p = 0.004). The postoperative JOA score and flexion angle were significantly higher in the LPF group than in the no-LPF group. LPF correlated with less incidence of postoperative AKP and improved the JOA score and knee flexion angle. In patellar resurfaced TKA, LPF may be considered an additional maneuver to avoid postoperative AKP.

Patient-Reported Outcomes of Minimally Invasive Distal Linear Metatarsal Osteotomy for Hallux Valgus.

BACKGROUND: Modified Bösch osteotomy, or distal linear metatarsal osteotomy (DLMO), is one of the minimally invasive correctional operations for hallux valgus deformity. Although the clinical and radiographic results of DLMO have been previously shown, the relationship between clinical outcomes using a validated patient-reported outcome measure and radiographic corrections have yet to be evaluated. METHODS: A total of 70 patients (97 feet) treated at our hospital were included in the study. The Self-Administered Foot Evaluation Questionnaire (SAFE-Q) and radiographic data were evaluated at a minimum 1-year follow-up. RESULTS: Scores of all five SAFE-Q subscales showed a statistically significant improvement: pain and pain-related (from 63.3 to 86.6), physical functioning and daily living (from 81.3 to 92.7), social functioning (from 79.5 to 94.4), shoe-related (from 43.1 to 72.3), and general health and well-being (from 67.7 to 92.1). The mean hallux valgus angle improved from 39.1° to 9.3°, and the mean intermetatarsal angle improved from 16.6° to 7.0°. Recurrence and hallux varus at the final follow-up occurred in nine feet (9.3%) and 15 feet (15.5%), respectively. Four of the five SAFE-Q subscale scores improved significantly even in patients with hallux varus. CONCLUSIONS: Distal linear metatarsal osteotomy improves foot-related quality of life in patients with hallux valgus deformity despite of the high rate of postoperative radiographic complication, especially hallux varus. Patients might be willing to tolerate mild hallux varus after DLMO, as indicated by patient-centered clinical results.

Pressurized carbon dioxide lavage reduces the incidence of a radiolucent line around the tibial component two years after total knee arthroplasty.

INTRODUCTION: In cemented total knee arthroplasty (TKA), pressurized carbon dioxide (CO2) lavage prior to cement fixation can eliminate debris at the bone-cement interface and is considered effective for increasing cement penetration and preventing aseptic loosening. Regarding the risk of a preliminary diagnosis of implant loosening, a radiolucent line (RLL) is a valuable sign. The purpose of this study was to compare the incidence of a tibial RLL at 2 years after TKA with and without pressurized CO2 lavage. METHODS: This is a retrospective study. One hundred knees from 98 patients were enrolled in this study. TKA was performed without pressurized CO2 lavage (CO2- group) for the first 47 knees, and with pressurized CO2 lavage (CO2+ group) for the next 53 knees. The depth of cement penetration was measured just after surgery, and the incidence of tibial RLL > 2 mm at 2 years after TKA was determined. RESULTS: Significant differences between groups were not seen regarding pre- and postoperative clinical factors. The depth of cement penetration in each area was significantly higher in the CO2+ group. The frequency of knees with RLL > 2 mm was significantly lower in the CO2+ group than in the CO2- group (p < 0.001). CONCLUSIONS: Pressurized CO2 lavage improved cement penetration and decreased the incidence of tibial RLL > 2 mm at 2 years after TKA.

Association between magnetic resonance imaging characteristics and pathological findings in entire posterior cruciate ligament with mucoid degeneration.

Magnetic resonance imaging (MRI) findings of a tram-track appearance and celery stalk appearance in mucoid degeneration of the cruciate ligament are valuable; however, their pathological basis is unclear. Because these appearances are generally seen throughout the entire ligament, the association between MRI findings and pathological findings must be verified in specimens of the whole degenerated ligament, including the ligamentous attachments to bone. We herein report two cases of mucoid degeneration of the posterior cruciate ligament with osteoarthritis of the knee requiring total knee arthroplasty. The entire degenerated ligament, including the ligamentous attachments to bone, was removed and pathologically evaluated. On pathological examination, the central portion of the lesion showed typical mucoid degeneration, whereas the marginal and adherent portions showed normal ligament tissue, consistent with a tram-track appearance on T2-weighted MRI. The fibrous normal ligament tissues in the longitudinal direction in regions of mucoid degeneration were consistent with a celery stalk appearance on T2-weighted MRI. No mucoid degeneration was found in the attachment area. The tram-track appearance and celery stalk appearance of mucoid degeneration on MRI can be explained by the pathological findings.

Optimal time period for blood glucose level evaluation after total knee arthroplasty in patients without diabetes: a prospective, observational study.

BACKGROUND: Postoperative hyperglycemia has been reported to be a risk factor for postoperative infection even in patients without diabetes mellitus (DM). However, there is no standard for how long blood glucose level (BGL) monitoring should be performed after total knee arthroplasty (TKA). The purpose of this study was to determine the optimal time period for BGL evaluation after TKA in patients without DM. METHODS: This prospective study included 132 knees of 110 patients who underwent TKA between March 2018 and July 2021 in our hospital. Fasting BGLs were measured preoperatively, at 9:00 PM on the day of surgery (DOS), and at 7:00 AM on postoperative days (PODs) 1, 2, and 3. Patients were divided into two groups with a preoperative hemoglobin A1c (HbA1c) cut-off value of 5.9%, and the BGLs on POD 1 were compared between the two groups. RESULTS: The BGLs were significantly higher on the DOS, POD 1, and POD 2 than preoperative levels. The BGL was significantly higher on POD 1 than at any other time point. Patients with an HbA1c ≥ 5.9% had significantly higher BGLs than those with an HbA1c < 5.9% on POD 1. CONCLUSIONS: The optimal time period for BGL evaluation after TKA in patients without DM was considered to be from postoperative to POD 2. Patients with an HbA1c ≥ 5.9% may require careful perioperative glycemic control.

Not Using a Tourniquet May Reduce the Incidence of Asymptomatic Deep Venous Thrombosis After ACL Reconstruction: An Observational Study.

BACKGROUND: Deep venous thrombosis (DVT) and pulmonary embolism are serious potential complications after anterior cruciate ligament reconstruction (ACLR). Little is known about the influence of tourniquet use on the incidence of DVT after ACLR. PURPOSE: To compare the incidence of DVT after ACLR with and without the use of a tourniquet. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: Between November 2018 and May 2020, a total of 60 consecutive ACLRs in 60 patients, including 7 revision surgeries, were performed without tourniquet use at our hospital and were enrolled in this study (T- group). In addition, 55 consecutive ACLRs in 55 patients, including 10 revision surgeries, were performed with tourniquet use between April 2017 and September 2018 and were enrolled as the control group (T+ group). DVT was diagnosed using ultrasonography of both legs performed preoperatively and at postoperative week 1. The incidence of postoperative DVT was compared between the T- and T+ groups. Logistic regression analysis was performed to evaluate the effect of older age (≥40 vs <40 years) and tourniquet use on the occurrence of DVT. RESULTS: No DVTs were detected preoperatively. The incidence of postoperative DVT was significantly lower in the T- group compared with the T+ group (1 patient [1.7%] vs 9 patients [16.4%]; P = .005). All patients with DVT were asymptomatic. Although the mean operative time was not significantly different (80.8 minutes in the T+ group vs 78.5 minutes in the T- group; P = .461), the mean blood loss from the drain was significantly lower in the T- group than in the T+ group (149.9 vs 201.9 mL; P < .001). Age ≥40 years and tourniquet use were significantly related to the occurrence of DVT (odds ratio, 8.3 [95% CI, 1.9-36.8]; P = .005; and odds ratio, 8.8 [95% CI, 1.0-75.3]; P = .047, respectively). CONCLUSION: ACLRs performed without tourniquet resulted in a significantly lower incidence of DVT after ACLR and significantly less bleeding from drains. If adequate visibility of the surgical field is obtained, ACLR without tourniquet use may reduce the incidence of DVT.

Suture Anchor Repair With Fully Threaded Knotless Anchors for Quadriceps Tendon Rupture Resulted in Favorable Outcomes After 2 Years.

PURPOSE: To investigate clinical outcomes over 2 years in cases of quadriceps tendon rupture (QTR) that were surgically treated using fully threaded knotless anchors. METHODS: A total of four knees in four male patients with QTR repaired with fully threaded knotless anchors at our hospital from November 2017 to January 2019 were enrolled. Mean patient age at surgery was 65.3 years (range: 61-70 years). Intraoperatively, stability of the sutured site was confirmed by knee flexion to 90°. Full weight walking with the orthosis in extension was commenced on the seventh postoperative day. Surgical findings, pathologies of the ruptured quadriceps tendons, and postoperative clinical outcomes were evaluated in all patients. RESULTS: The QTR was complete in three cases and partial in one. Average surgical duration was 58.5 (range: 49-74) minutes. Pathological evaluation revealed hyaline degeneration with granulation of the quadriceps tendon in two cases. No complications, such as infection and rerupture, occurred. Magnetic resonance imaging performed 1 year postoperatively confirmed complete healing of the repaired tendon. The mean follow-up period was 35.5 months (range: 24-46 months). None of the patients had extension lag of the knee, and mean Lysholm score and range of flexion were 95.3 (range: 85-100) and 141.3° (range: 140-145°), respectively, at the final follow-up. CONCLUSIONS: Clinical outcomes were favorable in all cases, including two cases with pathological degenerative changes. Suture anchor repair with fully threaded knotless anchors can be considered a minimally invasive and effective method for QTR, with sufficient strength to allow early rehabilitation.

Contraindication of Minimally Invasive Lateral Interbody Fusion for Percutaneous Reduction of Degenerative Spondylolisthesis: A New Radiographic Indicator of Bony Lateral Recess Stenosis Using I Line.

STUDY DESIGN: Retrospective cohort study. PURPOSE: This study aimed to evaluate aggravated lateral recess stenosis and clarify the indirect decompression threshold by combined lateral interbody fusion and percutaneous pedicle screw fixation (LIF/PPS). OVERVIEW OF LITERATURE: No previous reports have described an effective radiographic indicator for determining the surgical indication for LIF/PPS. METHODS: A retrospective review of 185 consecutive patients, who underwent 1- or 2-level lumbar fusion surgery for degenerative spondylolisthesis (DS). According to their symptomatic improvement, they were placed into either the "recovery" or "no-recovery" group. Preoperative computed tomography (CT) images were evaluated for the position of the superior articular processes at the slipping level, followed by a graded classification (grades 0-3) using the impingement line (I line), a new radiographic indicator. All 432 superior articular facets in 216 slipped levels were classified, and both groups' characteristics were compared. RESULTS: There were 171 patients (92.4%) in the recovery group and 14 patients in the no-recovery group (7.6%). All patients in the no-recovery group were diagnosed with symptoms associated with deteriorated bony lateral recess stenosis. All superior articular processes of the lower vertebral body in affected levels reached and exceeded the I line (I line-; grade 2 and 3) on preoperative sagittal CT images. In the recovery group, most superior articular processes did not reach the I line (I line+; grade 0 and 1; p=0.0233). CONCLUSIONS: In DS cases that are classified as grade 2 or greater, the risk of aggravated bony lateral recess stenosis due to corrective surgery is high; therefore, indirect decompression by LIF/PPS is, in principle, contraindicated.

Benign Neglect of Anomalous Insertion of the Anterior Horn of the Medial Meniscus as an Incidental Finding During Knee Arthroscopy.

PURPOSE: To evaluate the clinical results following arthroscopic surgery in patients with anomaly of the anterior horn of the medial meniscus (AHMM) that was found unexpectedly during surgery and discuss whether resection is necessary in patients without anteromedial knee pain (AMKP). METHODS: Between May 2014 and April 2017, a total of 387 knee arthroscopies in 379 patients were performed. Among these, 11 knees in 11 patients showed an anomalous insertion of the AHMM (incidence, 2.8%), and all 11 patients were included in this study. For these 11 patients, medical records including preoperative diagnosis, arthroscopic findings, and pre- and postoperative clinical evaluations were analyzed. RESULTS: None of the patients complained of AMKP before arthroscopy. Two patients were diagnosed with lateral meniscus injury and the other 9 patients were diagnosed with medial meniscus injury. All anomalies of the AHMM were found incidentally during arthroscopic surgery. The anomaly formed a band-like structure arising from the anterior portion of the medial meniscus and was attached to the anterior aspect of the ACL and femoral intercondylar notch. All 11 patients underwent partial meniscectomy, but anomalies of the AHMM were not resected. One patient was excluded from clinical evaluation, as that patient required subsequent total knee arthroplasty due to osteoarthritis. For the other 10 patients, mean follow-up was 36.8 months (range, 26-61 months). Knee pain was relieved, and none developed postoperative AMKP. Mean Lysholm score improved significantly from 55.9 to 91.2 (P < .001). CONCLUSIONS: The incidence of the anomaly was 2.8% in our study. If the patient has no AMKP before arthroscopic surgery, anomaly of the AHMM is a silent lesion that does not warrant resection. LEVEL OF EVIDENCE: Level IV, therapeutic case series.

Three-Dimensional Analysis of the First Metatarsal Bone in Minimally Invasive Distal Linear Metatarsal Osteotomy for Hallux Valgus.

BACKGROUND: Modified Bösch osteotomy (distal linear metatarsal osteotomy [DLMO]) is one of the minimally invasive correctional surgeries for hallux valgus. The 3-dimensional correctional angles and distances of the first metatarsal bone in DLMO have not been clarified. The purpose of this study was to analyze the 3-dimensional postoperative morphological changes of the first metatarsal bone in DLMO. METHODS: Twenty patients (30 feet) who underwent DLMO were enrolled. Preoperative plain radiographs and computed tomography (CT) scans of the feet were examined. Postoperative radiographs and CT scans were also obtained after bone union. The surface data of the pre- and postoperative first metatarsals were reconstructed from the CT data. The positions of the distal ends of the first metatarsals described with respect to the proximal ends were calculated using CT surface-matching technique. RESULTS: The distal end of the first metatarsal after DLMO was significantly supinated (10.2 ± 6.0 degrees, P < .001), adducted (6.0 ± 11.8 degrees, P = .004), dorsiflexed (11.1 ± 10.9, P < .001), shortened (7.4 ± 2.5 mm, P < .001), elevated (2.3 ± 3.1 mm, P = .001), and laterally shifted (8.2 ± 3.0 mm, P < .001) compared to the preoperative metatarsal distal end. Supination correction demonstrated a significant correlation with adduction correction (r = 0.659, P < .001) on correlation analyses between these parameters. CONCLUSION: The 3-dimensional corrections of the first metatarsal bone after DLMO were evaluated. Pronation and abduction were successfully corrected. Furthermore, adduction correction might be an important factor affecting correction of pronation. LEVEL OF EVIDENCE: Level IV, retrospective case series.

Minimally invasive distal linear metatarsal osteotomy combined with selective release of lateral soft tissue for severe hallux valgus.

BACKGROUND: Minimally invasive techniques for hallux valgus have been widely used to treat mild to moderate hallux valgus deformities. The purpose of this study was to evaluate the clinical and radiographic outcomes of distal linear metatarsal osteotomy (DLMO), which is one of the minimally invasive techniques, for severe hallux valgus. METHODS: 95 patients (141 feet) with severe hallux valgus underwent DLMOs. Lateral soft tissue release (LSTR) was performed at the same time for the cases selected by an original manual test. The satisfaction level, the Japanese Society of Surgery of the Foot (JSSF) hallux scale score, and weight-bearing radiographs of the foot were assessed preoperatively and after more than 24 months. In addition, the clinical and radiographic outcomes were compared among three groups divided by the kind of LSTR: no LSTR; manual correction; and open release through skin incision. RESULTS: Although the first metatarsal bone was significantly shortened, dorsiflexed, and elevated on postoperative radiographs, the rate of satisfaction was 87.2% (123/141), and the mean JSSF hallux scale score improved significantly from 60.4 (44-73) to 90.4 (65-100). The mean hallux valgus and intermetatarsal angles also improved significantly from 45.5° (40.0-60.0°) to 10.3° (-28.0-40.9°) and from 19.9° (14.0-28.7°) to 8.3° (-1.6-18.5°), respectively. Delayed union (18 feet), metatarsalgia (16 feet), recurrence (22 feet), and hallux varus (22 feet) were observed, and they were more obvious in DLMO combined with open release through a skin incision. CONCLUSIONS: DLMO combined selectively with LSTR is an effective procedure for correcting severe hallux valgus. However, the indication for open release with DLMO should be considered carefully.

Etiological factors in hallux valgus, a three-dimensional analysis of the first metatarsal.

BACKGROUND: It has been reported that hallux valgus (HV) is associated with axial rotation of the first metatarsal (1MT). However, the association between HV and torsion of the 1MT head with respect to the base has not been previously investigated. The present study examined whether there was a significant difference in 1MT torsion between HV and control groups. METHODS: Three-dimensional (3D) computed tomography (CT) scans of 39 ft were obtained, and 3D surface models of the 1MT were generated to quantify the torsion of the head with respect to the base. The HV group consisted of 27 ft from 27 women (69.5 ± 7.5 years old). Only the feet of HV patients with an HV angle >20° on weight-bearing radiography were selected for analysis. The control group consisted of 12 ft from 12 women (67.7 ± 7.2 years old). In a virtual 3D space, two unit vectors, which describe the orientation of the 1MT head and base, were calculated. The angle formed by these two unit vectors representing 1MT torsion was compared between the control and hallux valgus groups. RESULTS: The mean (± standard deviation) of the torsional angle of the 1MT was 17.6 (± 7.7)° and 4.7 (± 4.0)° in the HV and control groups, respectively, and the difference was significant (p < 0.01). CONCLUSIONS: This is the first study, to the best of our knowledge, to investigate 1MT torsion in HV patients using CT-based 3D analysis. The 1MT showed significant eversion in hallux valgus patients compared to control group patients.

A missense single nucleotide polymorphism in the ALDH2 gene, rs671, is associated with hip fracture.

Hip fracture is the most severe bone fragility fracture among osteoporotic injuries. Family history is a known risk factor for fracture and now included among criteria for osteoporosis diagnosis and treatment; however, genetic factors underlying family history favoring fracture remain to be elucidated. Here we demonstrate that a missense SNP in the ALDH2 gene, rs671 (ALDH2*2), is significantly associated with hip fracture (odds ratio = 2.48, 95% confidence interval: 1.20-5.10, p = 0.021). The rs671 SNP was also significantly associated with osteoporosis development (odds ratio = 2.04, 95% confidence interval: 1.07-3.88, p = 0.040). For analysis we enrolled 92 hip fracture patients plus 48 control subjects without bone fragility fractures with higher than -2.5 SD bone mineral density. We also recruited 156 osteoporosis patients diagnosed as below -2.5 SD in terms of bone mineral density but without hip fracture. Association of rs671 with hip fracture and osteoporosis was significant even after adjustment for age and body mass index. Our results provide new insight into the pathogenesis of hip fracture.

Delayed Propionibacterium acnes surgical site infections occur only in the presence of an implant.

Whether Propionibacterium acnes (P. acnes) causes surgical-site infections (SSI) after orthopedic surgery is controversial. We previously reported that we frequently find P. acnes in intraoperative specimens, yet none of the patients have clinically apparent infections. Here, we tracked P. acnes for 6 months in a mouse osteomyelitis model. We inoculated P. acnes with an implant into the mouse femur in the implant group; the control group was treated with the bacteria but no implant. We then observed over a 6-month period using optical imaging system. During the first 2 weeks, bacterial signals were detected in the femur in the both groups. The bacterial signal completely disappeared in the control group within 28 days. Interestingly, in the implant group, bacterial signals were still present 6 months after inoculation. Histological and scanning electron-microscope analyses confirmed that P. acnes was absent from the control group 6 months after inoculation, but in the implant group, the bacteria had survived in a biofilm around the implant. PCR analysis also identified P. acnes in the purulent effusion from the infected femurs in the implant group. To our knowledge, this is the first report showing that P. acnes causes SSI only in the presence of an implant.