OBJECTIVE: Transient osteoporosis of the hip (TOH) is an uncommon, typically self-limited diagnosis of uncertain etiology. We hypothesize that TOH represents an underlying subchondral fracture, and a discrete fracture line can often be detected on high-resolution MRI.
METHODS: A retrospective PACS query identified patients meeting imaging criteria for TOH with intense bone marrow edema (BME) in the femoral head on MRI. Those with poor quality studies, other underlying pathologies, or antecedent trauma were excluded. Three musculoskeletal radiologists independently reviewed each case for presence of a definite subchondral fracture line on small field of view (FOV) MR images of the affected hip. Extent of BME, reciprocal acetabular BME, and joint effusion size were also recorded. Binomial logistic regression was performed to determine statistically significant predictors of subchondral fracture.
RESULTS: Fifty patients met inclusion criteria (29 females, 0 pregnant). Mean age was 62±12 years (range 35-84). Average duration of symptoms before MRI was 102±135 days. Ten patients had bone densitometry within 2 years of MRI, six demonstrating osteopenia or osteoporosis. Subchondral fractures were unanimously identified in 44/50 (88%). Interclass correlation coefficient with absolute agreement was 0.73, 95% CI (0.57-0.84), indicating near-excellent agreement. Most cases demonstrated a large joint effusion (23/50, 46%) and acetabular BME (31/50, 62%). Increasing size of joint effusion was a statistically significant predictor of subchondral fracture (p=0.05), with 6.9 higher odds. There was a strong correlation with osteopenia/osteoporosis and fracture (p<0.001).
CONCLUSIONS: Discrete subchondral fractures were identified unanimously on small FOV imaging in the majority of TOH cases.

Osteochondritis dissecans (OCD) is a disease of the joints characterized by idiopathic focal subchondral lesions. Aggrecan, a proteoglycan encoded by the ACAN gene, is important for cartilage structure and function. We describe the clinical evolution of a patient with short stature, multi-focal OCD, and subchondral osteopenia that appeared linked to a novel pathogenic ACAN variant. A multi-disciplinary approach including medical (bisphosphonate) therapy, surgical intervention and rehabilitation were successful in restoring wellness and physical function.

The purpose of our study was the clinical characteristics, radiographic appearance, and outcomes after treatment in patients with rapid destructive arthrosis (RDA) due to subchondral insufficiency fracture (SIF) of the shoulder. Twenty-two cases of RDA of the shoulder were retrospectively reviewed. Clinical outcomes for 15 cases who underwent shoulder arthroplasty were evaluated at an average of 41.4 months. The mean age of patients was 73.7 years (range 50-83 years), and there were 20 women and 2 men. The mean time from onset of symptoms to head collapse was 6.8 months (range 1-12 months). The mean t-score of bone mineral density was -3.1. Nine patients had pseudoparalysis. Based on radiographic appearance, a diversity of types of head destruction with subchondral fracture, bone marrow edema, joint effusion, and synovitis were observed in all cases. In conclusion, RDA due to SIF of the shoulder, presenting with severe short-term pain and functional disability, commonly occurred in elderly women with bone fragility. MRI revealed bone marrow edema, extensive joint effusion, and synovitis as well as a diversity of types of head destruction with subchondral fracture within several months from onset of symptoms.

Timing of surgery is the most critical prognostic factor for hip osteonecrosis treated with free vascularized fibular grafting (FVFG). Bone marrow lesion (BML) on MRI usually occurs immediately before femoral head collapse. We conducted a retrospective cohort study to evaluate whether the noncollapsed hips with BML can benefit from FVFG.
Consecutive patients undergoing modified FVFG were identified from our clinical repository between January 2014 and December 2014. Based on whether BML was pre-operatively detected, the four year radiographic and clinical outcomes were compared.
In the BML cohort, 22 of 53 hips (42%) showed radiographic signs of osteonecrosis progression, which was significantly higher than that in the control cohort (8 of 49, 16%; P = 0.005). The BML hips showed a significantly lower pre-operative Harris Hip Score (HHS) than those without BML (77.8 vs. 85.5, P = 0.046), whereas no such difference was observed in the final HHS or its post-operative improvement (HHS 90 vs. 94, P = 0.397; HHS improvement 12 vs. 8, P = 0.067). In the subgroup of patients with a pre-operative HHS lower than 80, BML hips were associated with a slightly lower final HHS than hips without BML. Four of 5 (80%) failed hips with BML had a poor pre-operative hip function.
BML indicates the last chance for a reproducible improvement in the treatment of hip osteonecrosis with FVFG before collapse. However, the concomitant lower pre-operative HHS (< 80) is a poor prognostic factor for BML-positive hips.

This paper is a commentary on the article entitled \"Nomenclature of Subchondral Nonneoplastic Bone.Lesions1\" by Gorbachova, Amber, Beckmann, Bennett, Chang, Davis, Gonzalez, Hansford, Howe, Lenchik, Winalski, and Bredella. The purpose of this commentary is to provide an orthopaedic perspective on the aforementioned article and critique their analysis and proposal regarding nomenclature of subchondral bone lesions. It provides an overview and a section by section evaluation of a well-designed and executed article.

BACKGROUND: Causality for postarthroscopic osteonecrosis of the knee is unknown, and related mechanisms have been poorly characterized.
METHODS: This report describes a case of a 69-year-old man with subchondral fracture occurring after arthroscopic meniscectomy using a radiofrequency assisted shaver. The patient experienced increasingly intense knee pain 10 months after the meniscectomy. MR imaging revealed postarthroscopic osteonecrosis of the knee in the femoral medial condyle, requiring unicompartmental knee arthroplasty. A mid-coronal cut section of the resected medial femoral condyle showed a linear fracture line parallel to the subchondral bone endplate. Histopathological examination showed prominent callus formation on both sides of the fracture, comprised of reactive woven bone and granulation tissue. The middle portion of the resected medial meniscus was of uneven height, with significant stiffening of the higher side. The stiffened region of the medial meniscus corresponded to the subchondral fracture in the medial femoral condyle.
CONCLUSIONS: The etiology of post-arthroscopic osteonecrosis of the knee is controversial, but it seems possible that altered knee biomechanics after meniscectomy may predispose patients to osteonecrosis. The findings of the current case suggested that uneven stiffening of the meniscus caused concentration of stress that resulted in postarthroscopic subchondral fracture.
CONCLUSIONS: Subchondral insufficiency fracture following arthroscopy may be underdiagnosed. Surgeons need to carefully consider the risk of subchondral fracture following uneven stiffening of the meniscus when to use radiofrequency in the debridement of a torn meniscus.

BACKGROUND: Rapidly destructive arthropathy (RDA) of the shoulder is rare. Consequently, there are very few studies that have reported the characteristic findings of this disease. This study aimed to analyze the clinical, radiographic, and histologic features of patients with RDA of the shoulder.
METHODS: In total, 9 cases (8 patients) were enrolled in this study. All patients were elderly women, with a mean age of 72.7 years (range, 57-78 years). The mean duration of symptoms was 4.1 months (range, 1.2-5.9 months). Reverse total shoulder arthroplasty and total shoulder arthroplasty were performed in 5 cases with massive rotator cuff tears and 4 without them, respectively.
RESULTS: The mean duration of radiologically evident joint destruction after negative results on radiography was 3.1 months (range, 1.0-5.9 months). On plain radiography, humeral head flattening and collapse that appeared like cut grass were observed (100%). Relatively good preservation of the glenoid with a normal joint space was observed in 7 cases, whereas glenoid erosion was observed in 2 (22.2%). T1-weighted magnetic resonance imaging showed a subchondral fracture (100%) of low signal intensity with associated bone marrow edema. Histologically, chronic inflammation of the synovium and osteocytes in the lacunae, as well as callus formation, were observed along the subchondral fracture.
CONCLUSIONS: Flattening and collapse of the humeral head within an average of 4 months of symptom onset are characteristic of RDA of the shoulder. Bone marrow edema, joint effusion, and subchondral fracture on magnetic resonance imaging and fracture fragments and callus formation on histopathologic analysis were observed. Glenoid erosion was observed in 2 cases with arthrosis progression.

Stress distribution remains unclear in early-stage osteonecrosis of the femoral head (ONFH). To clarify this issue, we generated patient-specific finite element models (FEMs) from 51 patients with ONFH. Patients\' hips were classified into three groups: ONFH without a sclerotic boundary (Stage 1, n = 6), ONFH with a sclerotic boundary (Stage 2, n = 10), and ONFH with both a sclerotic boundary and <2 mm collapse (Stage 3, n = 35). Four hips without ONFH were used as controls. Stress distribution in each FEM was compared with magnetic resonance imaging (MRI) and computed tomography (CT) results. Fifteen wholly resected femoral heads in Stage 3 hips were assessed by micro-CT. Furthermore, we histologically examined three Stage 2 femoral heads that subsequently developed subchondral fractures after FEM analyses. In all FEMs of both control and Stage 1 hip, stress was equally distributed on the femoral head surface. However, in all FEMs of both Stages 2 and 3 hips, stress was concentrated at the lateral boundary of the femoral head surface, corresponding to both a low-intensity band on T1-weighted MRI images and sclerotic changes on CT. On micro-CT, subchondral fractures consistently began at the lateral boundary with sclerotic changes, in which bone volume fraction was increased. Histology showed breakage of subchondral plates at the junction between necrotic and reparative zones. In early-stage ONFH, sclerotic changes caused stress concentration, which can trigger subchondral fractures at the lateral boundary. Clinical Significance: Our results will clarify the pathogenic mechanism of collapse in ONFH. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3169-3177, 2018.

For successful joint preservation in osteonecrosis of the femoral head (ONFH), it is important to understand the mechanism of collapse. The purpose of this study was to investigate the initiation of subchondral fracture in ONFH by using micro-CT imaging of the whole femoral head, focusing on the three-dimensional relationship between the subchondral fracture and the bone resorption area.
A total of 40 femoral heads from 37 patients retrieved during total hip arthroplasty for stage 3A or 3B ONFH by Japanese Investigation Committee criteria were scanned using micro-CT with a 0.146-mm thickness cuts. We divided the cohort into early and late collapsed stages according to a threshold of 3 mm of collapse as measured by micro-CT.
According to the analysis on multiple radial plane views in the whole femoral head, there were two interesting findings. First, the initial fracture cracks ran between separated bone resorption areas at the anterosuperior portions of all 18 femoral heads in the early collapsed stage. Second, fractures of the necrotic bone at the sclerotic boundary and a fibrous, granulation-like, low-density tissue along the necrotic side of the sclerotic boundary were seen in 19 of the 22 in the late collapsed stage. After bone resorption around the retinaculum and teres insertion initiates the subchondral fracture, bone resorption expanding at the anterosuperior portion of the femoral head may result in the spread of fracture and the potential for massive collapse.
Three-dimensional micro-CT showed bone resorption around the reparative zone initiates the subchondral fracture in ONFH.

OBJECTIVE: The purpose of this paper is to review the distinct clinical and radiographic features that may lead to prompt diagnosis of rapidly progressive osteoarthritis (RPOA) and thus obviate unnecessary and costly diagnostic workup.
RESULTS: RPOA is uncommon but is more frequently seen in practice because of the aging population. RPOA is a destructive arthropathy that occurs most commonly in elderly women but can also be seen in patients that have sustained trauma. The dramatic radiologic manifestations of RPOA can lead to diagnostic confusion with other arthropathies, infection, and osteonecrosis. RPOA was originally described in the hip but may also involve the shoulder. The etiology of RPOA is not well understood, but subchondral fracture probably plays a role in the development of dramatic destruction of the joint that is seen in affected patients. Early diagnosis may reduce the complexity of surgical management. RPOA is an uncommon condition that occurs most frequently in elderly woman or in patients who have sustained trauma. Prompt recognition of the clinical and radiologic features of this arthropathy can reduce unnecessary diagnostic workup and complexity of surgical intervention.