Histopathological Confirmation of Axonal Sprouting in Regenerative Peripheral Nerve Interface.

Symptomatic neuroma represents a debilitating complication after major limb amputation. The regenerative peripheral nerve interface (RPNI) has emerged as a reproducible and practical surgery aimed at mitigating the formation of painful neuroma. Although previous animal studies revealed axonal sprouting, elongation, and synaptogenesis of proximal nerve stump within the muscle graft in RPNI, there is a lack of reports confirming these physiological reactions at the histopathological level in human samples. This report presents a case of below-knee amputation with RPNI due to foot gangrene resulting from polyarteritis nodosa. Subsequently, an above-knee amputation was necessitated due to the exacerbation of polyarteritis nodosa, providing the opportunity for histopathological examination of the RPNI site. The examination revealed sprouting, elongation, and existence of neuromuscular junction of the tibial nerve within the grafted muscle. To the best of our knowledge, this is the first report demonstrating axonal sprouting, elongation, and possibility of synaptogenesis of the nerve stump within the grafted muscle in a human sample.

Short-Term Risk Factors for Subtalar Arthrodesis After Primary Tibiotalar Arthrodesis.

While adjacent joint arthritis is a recognized long-term downside of primary tibiotalar arthrodesis (TTA), few studies have identified risk factors for early subtalar arthrodesis (STA) after TTA. This study aims to identify the risk factors for STA within the first few years following TTA. All patients older than 18 years undergoing TTA between 2008 and 2016 were identified retrospectively. Demographic data and comorbidities were collected alongside prior operative procedures, postoperative complications, and subsequent STA. Pre-and postoperative Kellgren-Lawrence osteoarthritis grade of the subtalar joint and postoperative radiographic alignment were obtained. A total of 240 patients who underwent primary TTA were included in this study with median follow up of 13.8 months. Twenty patients (8.3%) underwent STA after TTA due to symptomatic nonunion of TTA in 13 (65%), progression of symptomatic subtalar osteoarthritis (OA) in 4 (20%), and symptomatic nonunion of primary TTA combined progressively symptomatic subtalar OA in 2 (10%). Preoperative radiographic subtalar OA severity and postoperative radiographic alignment were not correlated with subsequent STA. Diabetes mellitus, Charcot arthropathy, neuropathy, alcohol use, substance use disorder, and psychiatric disease were significantly associated with having a subsequent STA. The most common postoperative contributing factor for subsequent STA following primary TTA was the salvage of symptomatic ankle nonunion rather than subtalar joint disease. Patients considering an ankle fusion should be counseled of the risk of subsequent STA, especially if they have risk factors that include diabetes, Charcot arthropathy, neuropathy, alcohol use, substance use disorder, or psychiatric disease.

Runx2 and Runx3 differentially regulate articular chondrocytes during surgically induced osteoarthritis development.

The Runt-related transcription factor (Runx) family plays various roles in the homeostasis of cartilage. Here, we examined the role of Runx2 and Runx3 for osteoarthritis development in vivo and in vitro. Runx3-knockout mice exhibited accelerated osteoarthritis following surgical induction, accompanied by decreased expression of lubricin and aggrecan. Meanwhile, Runx2 conditional knockout mice showed biphasic phenotypes: heterozygous knockout inhibited osteoarthritis and decreased matrix metallopeptidase 13 (Mmp13) expression, while homozygous knockout of Runx2 accelerated osteoarthritis and reduced type II collagen (Col2a1) expression. Comprehensive transcriptional analyses revealed lubricin and aggrecan as transcriptional target genes of Runx3, and indicated that Runx2 sustained Col2a1 expression through an intron 6 enhancer when Sox9 was decreased. Intra-articular administration of Runx3 adenovirus ameliorated development of surgically induced osteoarthritis. Runx3 protects adult articular cartilage through extracellular matrix protein production under normal conditions, while Runx2 exerts both catabolic and anabolic effects under the inflammatory condition.

The discrepancy between radiographically-assessed and self-recognized hallux valgus in a large population-based cohort.

BACKGROUND: There has been a paucity of literature revealing the discrepancy between self-recognition about hallux valgus (HV) and radiographically-evaluated foot configuration. Knowing this discrepancy will help to make a comparative review of the findings of previous literatures about epidemiological studies about the prevalence of HV. QUESTIONS/PURPOSES: (1) Is there a discrepancy between radiographically-assessed and self-recognized HV in the general population? (2) What factors affect the self-recognition of HV in the general population? METHODS: The fifth survey of the Research on Osteoarthritis/Osteoporosis against Disability study involved 1996 participants who had undergone anterior-posterior radiography of bilateral feet and answered a simple dichotomous questionnaire on self-recognition of HV. Measurements of the HV angle (HVA), interphalangeal angle of the hallux (IPA), and intermetatarsal angle between 1st and 2nd metatarsals (IMA) were performed using radiographs. Radiographic diagnosis of HV was done using the definition of hallux valgus angle of 20° or more. After univariate comparison of the participant backgrounds and radiographic measurements between participants with or without self-recognition of HV, multivariable logistic regression analysis was conducted in order to reveal independent factors affecting self-recognition. RESULTS: Significant difference was found between the prevalence of radiographically-assessed and self-recognized HV (29.8% vs. 16.5%, p <  0.0001). The prevalence of self-recognized HV increased with the progression of HV severity from a single-digit percentage (normal grade, HVA < 20°) up to 100% (severe grade, HVA ≥ 40°). A multivariable logistic regression analysis demonstrated that HVA, IMA, and female sex were independent positive factors for self-recognition of HV (HVA [per 1° increase]: OR, 1.18; 95% CI, 1.15-1.20; p <  0.0001; IMA [per 1° increase]: OR, 1.15; 95% CI, 1.09-1.20; p <  0.0001; and female sex [vs. male sex]: OR, 3.47; 95% CI, 2.35-5.18; p <  0.0001). CONCLUSIONS: There was a significant discrepancy between radiographically-assessed and self-recognized HV which narrowed with the progressing severity of HV. HVA, IMA, and female sex were independent positive factors for self-recognition of HV. Attention needs to be paid to potentially lowered prevalence of HV in epidemiological studies using self-reporting based on self-recognition.

Effect of gait protocols and postoperative shoes on off-loading of forefoot in preoperative patients for forefoot disorders.

OBJECTIVES: The purpose of this study was to clarify the effect of gait protocols and postoperative shoes on forefoot load in preoperative patients for forefoot disorders and compare footwear comfort between different types of postoperative shoes. METHODS: Fourteen subjects scheduled to undergo forefoot surgeries were recruited. The maximum force under the forefoot region was measured during 10 m straight walking in two gait patterns with six different shoe types. Visual analogue scale (VAS) scores for footwear comfort, subjective lower thigh pain, and electrical activities of lower thigh muscles were also evaluated. RESULTS: The body weight-normalized maximum force under the forefoot region significantly decreased in step-to gait compared to normal gait regardless of the shoe types used. Under the same gait condition, no significant difference was observed in the forefoot off-loading effect between the different shoe types used. Significantly worse VAS scores, significantly higher tibialis anterior muscle activities, and complaints of lower thigh pain were demonstrated in the gait with the reverse camber shoe. CONCLUSIONS: Gait protocol of step-to gait had more forefoot off-loading effect than postoperative shoes. The forefoot off-loading effect did not differ among the postoperative shoes, suggesting that postoperative shoes can be selected with an emphasis on footwear comfort.

Comparison between suture and staple fixations as internal fixation techniques for Akin osteotomy.

BACKGROUND: Suture and staple fixations are commonly used methods for Akin osteotomy; however, there has been a paucity of studies comparing these methods without bias. PATIENTS AND METHODS: We retrospectively compared the outcomes of 58 Akin osteotomies performed by a single surgeon using suture fixation and 39 Akin osteotomies performed by the same surgeon using staple fixation during the same period. RESULTS: Bone union at the osteotomy site was achieved in all cases with no cases of complications related to the materials used. Occurrence of breakage of the lateral cortex of the proximal phalanx showed no significant difference between the suture and staple groups. The lateral cortex breakage produced greater instability at the osteotomy site with the staple fixation compared to the suture fixation. CONCLUSIONS: Comparison of suture and staple fixations of Akin osteotomy demonstrated the superiority of suture fixation against staple fixation in terms of stability and cost-efficiency.

Clinical Outcomes After First Metatarsophalangeal Joint Arthrodesis by Flat Cut Joint Preparation With Individual Adjustment for Sagittal Alignment.

Sagittal misalignment is a major cause of patient dissatisfaction and re-operation after first metatarsophalangeal (MTP) joint arthrodesis. The stereotypical application of the fixed angle would be undesirable, especially in cases of flat or cavus foot. We retrospectively reviewed 31 cases (27 patients) in which first MTP joint arthrodesis was performed using the flat cut joint preparation technique with reference to the plantar clearance beneath the pulp of the toe while simulating weightbearing by pushing a board against the sole. The most common underlying cause of surgery was rheumatoid arthritis (22 cases [71%]). Clinical outcomes were evaluated by the Japanese of Surgery of the Foot (JSSF) hallux scale and the self-administered foot evaluation questionnaire (SAFE-Q). Twenty-three cases were also examined by pedobarography to evaluate postoperative walking plantar pressure. At the most recent follow-up of a mean 19.6 months, the toe-to-floor distance of the hallux in static standing posture was a mean of 2.5 mm (range, 0-10 mm). All but 1 foot (97%) achieved bone union. There were no complications or revisions due to misalignment of the fused MTP joint. JSSF hallux scales improved significantly from 47 preoperatively to 82 postoperatively. All subscale scores except general health and well-being in the SAFE-Q improved significantly at final follow-up versus preoperative period. Plantar pressure under the hallux was correlated with the toe-to-floor distance but not radiographic parameter. In conclusion, first MTP joint arthrodesis achieved good clinical outcomes when using toe-to-floor distance and Kirschner wire template for flat cut joint preparation.

Symptomatic Medial Bone Excrescence in the Distal Phalanx of the Hallux after the First Metatarsophalangeal Joint Arthrodesis: A Case Report and Radiographic Reviews.

Medial bone excrescence at the base of the distal phalanx of the hallux is a common manifestation which is rarely painful. In this case report, we described the first case of the excrescence becoming symptomatic one year after a metatarsophalangeal (MTP) joint arthrodesis of the great toe in a 74-year-old female. The medial bony excrescence which was obscure preoperatively became obvious postoperatively in the anteroposterior foot radiographs. The patient was successfully treated by an excision of the excrescence. In order to clarify the pathology of the excrescence, we reviewed the radiographs with respect to the excrescence before and after hallux surgeries including 97 metatarsal osteotomies and 33 MTP joint arthrodesis. The width of the excrescence measured in the anteroposterior foot radiographs displayed substantial increment one month after the hallux surgeries (osteotomy group: 0.9 ± 0.7 vs. 1.5 ± 0.7 mm, p < 0.01; arthrodesis group: 1.3 ± 0.8 vs. 1.8 ± 1.0 mm, p < 0.01). However, there was no significant difference in the width of the excrescence between one month after surgery and at the most recent follow-up of around 20 months in average after the surgery (osteotomy group: 1.5 ± 0.7 vs. 1.4 ± 0.7 mm, p = 0.62; arthrodesis group: 1.8 ± 1.0 vs. 1.8 ± 0.7 mm, p = 0.37). The present case and our radiographic review suggested that the postoperative medial bony excrescence was not the result of change of position of the preexisting excrescence. The correction of pronation deformity through hallux surgeries could emphasize the medial bony excrescence and cause symptomatic irritation upon shoe contact.

Outcomes of Scarf and Akin Osteotomy with Intra-Articular Stepwise Lateral Soft Tissue Release for Correcting Hallux Valgus Deformity in Rheumatoid Arthritis.

BACKGROUND: The effectiveness of scarf and Akin osteotomy with intra-articular lateral soft tissue release for the correction of hallux valgus (HV) in patients with rheumatoid arthritis (RA) has not been elucidated. METHODS: A total of 36 feet in 28 patients with RA who had scarf and Akin osteotomy with intra-articular stepwise lateral soft tissue release between 2015 and 2020 at a single institute were investigated retrospectively, with a mean follow-up period of 32.0 ± 16.9 months. Radiographic evaluations including the HV angle, intermetatarsal angle, and sesamoid position were performed preoperatively and postoperatively. Clinical outcomes were assessed using the Japanese Society of Surgery of the Foot (JSSF) hallux scale and self-administered foot evaluation questionnaire (SAFE-Q). RESULTS: The procedure resulted in significant HV correction, with a recurrence rate of 13.9%. The JSSF scale and all five SAFE-Q subscale scores significantly improved (p < 0.05), with no major complications. More than 90% of cases achieved adequate lateral soft tissue release without sacrificing the adductor tendon of the hallux. CONCLUSIONS: Intra-articular stepwise lateral soft tissue release in combination with scarf and Akin osteotomy provided satisfactory radiographic and patient-reported outcomes for the correction of HV in patients with RA with minimum lateral soft tissue release.

Juvenile Dysplasia Epiphysealis Hemimelica with Multiple Ankle Free Body.

Dysplasia epiphysealis hemimelica (DEH), also known as Trevor's disease, is a rare overgrowth of cartilage that commonly arises in the epiphyseal bone of children. We report a rare case of DEH originating from a talus accompanied by multiple intra-articular free bodies in a 7-year-old patient with ankle instability. After the primary surgery for free body removal and microfracture technique for the cartilage defects in the ankle joint, the free body recurred. Secondary surgery of arthroscopic free body removal with lateral ankle ligament repair succeeded in treating the patient, without further recurrence of the free body.

Lubricin Contributes to Homeostasis of Articular Cartilage by Modulating Differentiation of Superficial Zone Cells.

Lubricin encoded by the proteoglycan 4 (Prg4) gene is produced from superficial zone (SFZ) cells of articular cartilage and synoviocytes, which is indispensable for lubrication of joint surfaces. Loss-of-function of human and mouse Prg4 results in early-onset arthropathy accompanied by lost SFZ cells and hyperplastic synovium. Here, we focused on increases in the thickness of articular cartilage in Prg4-knockout joints and analyzed the underlying mechanisms. In the late stage of articular cartilage development, the articular cartilage was thickened at 2 to 4 weeks and the SFZ disappeared at 8 weeks in Prg4-knockout mice. Similar changes were observed in cultured Prg4-knockout femoral heads. Cell tracking showed that Prg4-knockout SFZ cells at 1 week of age expanded to deep layers after 1 week. In in vitro experiments, overexpression of Prg4 lacking a mucin-like domain suppressed differentiation of ATDC5 cells markedly, whereas pellets of Prg4-knockout SFZ cells showed enhanced differentiation. RNA sequencing identified matrix metalloproteinase 9 (Mmp9) as the top upregulated gene by Prg4 knockout. Mmp9 expressed in the SFZ was further induced in Prg4-knockout mice. The increased expression of Mmp9 by Prg4 knockout was canceled by IκB kinase (IKK) inhibitor treatment. Phosphorylation of Smad2 was also enhanced in Prg4-knockout cell pellets, which was canceled by the IKK inhibitor. Expression of Mmp9 and phosphorylated Smad2 during articular cartilage development was enhanced in Prg4-knockout joints. Lubricin contributes to homeostasis of articular cartilage by suppressing differentiation of SFZ cells, and the nuclear factor-kappa B-Mmp9-TGF-ß pathway is probably responsible for the downstream action of lubricin. © 2020 American Society for Bone and Mineral Research (ASBMR).

Lateral Heel Pain Caused by Impingement of Hypertrophic Peroneal Tubercle and Os Peroneum.

Hypertrophic peroneal tubercle (HPT) is an overgrowth of the peroneal tubercle located on the lateral aspect of the hindfoot, which could cause tenosynovitis of the peroneus longus tendon. Os peroneum (OP) is an accessory ossicle that exists in the peroneus longus tendon at the lateral aspect of the calcaneocuboid joint. Both HPT and OP can cause lateral foot pain and occasionally require surgical treatment. We encountered a case of lateral foot pain of HPT coexisting with OP. Careful preoperative magnetic resonance imaging, dynamic ultrasonographic image, and block injection suggested an impingement of HPT and OP as a cause of lateral foot pain. Surgical resection of HPT, while retaining OP, successfully achieved pain relief in the patient. To the best of our knowledge, this is the first report presenting a case of HPT coexisting with OP successfully treated without OP resection.

Diagnosis and Treatment of Chronic Lateral Ankle Instability: Review of Our Biomechanical Evidence.

Definitive diagnosis and optimal surgical treatment of chronic lateral ankle instability remains controversial. This review distills available biomechanical evidence as it pertains to the clinical assessment, imaging work up, and surgical treatment of lateral ankle instability. Current data suggest that accurate assessment of ligament integrity during physical examination requires the ankle to ideally be held in 16° of plantar flexion when performing the anterior drawer test and 18° of dorsiflexion when performing the talar tilt test, respectively. Stress radiographs are limited by their low sensitivity, and MRI is limited by its static nature. Surgically, both arthroscopic and open repair techniques appear biomechanically equivalent in their ability to restore ankle stability, although sufficient evidence is still lacking for any particular procedure to be considered a superior construct. When performing reconstruction, grafts should be tensioned at 10 N and use of nonabsorbable augmentations lacking viscoelastic creep must factor in the potential for overtensioning. Anatomic lateral ligament surgery provides sufficient biomechanical strength to safely enable immediate postoperative weight bearing if lateral ankle stress is neutralized with a boot. Further research and comparative clinical trials will be necessary to define which of these ever-increasing procedural options actually optimizes patient outcome for chronic lateral ankle instability.

Association between fall history and performance-based physical function and postural sway in patients with rheumatoid arthritis.

OBJECTIVES: Patients with rheumatoid arthritis (RA) are at increased risk of falling; therefore, fall prevision and prevention are critical. The present study aimed to evaluate the ability of physical performance assessments to discriminate between RA patients with and without a history of falling. METHODS: Fifty patients with RA were divided into two groups according to the presence or absence of a history of falls within the previous 1 year. Physical performance was assessed using the short physical performance battery (SPPB), which consists of the timed standing balance, gait speed, and chair stand tests. Standing balance was also assessed as postural sway using a force platform in several positions including standing with both feet together, semitandem, and tandem. Backgrounds, SPPB, and postural sway were compared between the two groups. RESULTS: Fourteen patients (28%) reported one or more falls within the previous year. There were no significant intergroup differences in baseline characteristics or SPPB score. The group with a history of falls had significantly longer measured time for the 5-repetition chair stand test and significantly longer postural sway in the semitandem position. The discriminate analysis revealed that 5-repetition chair stand test or its combination with postural sway in the semitandem position significantly discriminated between fallers and non-fallers. CONCLUSION: Numerical evaluation of the chair stand test and postural sway in the semitandem position seems more appropriate than SPPB for assessing the fall risk of patients with RA.

The Effect of Gastrocnemius Recession and Tendo-Achilles Lengthening on Adult Acquired Flatfoot Deformity Surgery: A Systematic Review.

The purpose of this study was to evaluate the available clinical and radiographic evidence for incorporation of a gastrocnemius recession or tendo-Achilles lengthening into the surgical correction of adult acquired flatfoot deformity. A systematic review of the literature was performed using PubMed, Embase, Cochrane, CINAHL, and Google Scholar. Among the relevant articles, the level of evidence and quality was identified using the Methodological Index for Non-Randomized Studies tool. No study explicitly examined whether clinical or radiographic outcomes after adult acquired flatfoot deformity correction are improved when incorporating a gastrocnemius recession or tendo-Achilles lengthening compared with when no such procedure is performed, nor have they directly compared outcomes between 2 procedures. Studies demonstrated an overall improvement in postoperative range of motion and plantar flexion power after gastrocnemius recession, but such findings are hard to separate from the clinical contribution of concomitant corrective procedures to the foot itself. All studies that analyzed anteroposterior talo-calcaneal angle, anteroposterior lateral talo-first metatarsal angle and calcaneal inclination angle revealed improvement of each parameter postoperatively. There were no high-level evidence studies in the literature explicitly quantifying ankle range of motion, plantar flexion power, or radiographic impact of gastrocnemius recession or tendo-Achilles lengthening on adult acquired flatfoot deformity correction. Although gastrocnemius-soleus complex contractures have certainly been demonstrated to coexist with adult acquired flatfoot deformity, support for lengthening procedures is largely based on expert opinion or case series and is difficult to distinguish from the clinical contribution of associated corrective procedures.

Joint-Preserving Surgery for Hyperextension Deformity of the Hallux Interphalangeal Joint in a Patient with Rheumatoid Arthritis.

Interphalangeal hyperextension is one of the major hallux deformities in patients with rheumatoid arthritis; however, there is yet no established surgical method for this deformity. We here present the case of a 69-year-old female patient with rheumatoid arthritis who developed hallux interphalangeal hyperextension and painful callosity on the plantar hallux accompanied by limited dorsiflexion at the metatarsophalangeal joint. Lateral weight-bearing radiograph of the foot revealed misalignment of the medial column and hallux, including a collapsed medial arch, elevated first metatarsal, plantar flexion and deviation of the proximal phalanx, and hyperextension of the distal phalanx. The foot was successfully treated and became symptom-free with opening wedge osteotomy of the medial cuneiform, plantar and proximal translation of the metatarsal head, and tenotomy of the extensor hallucis longus. This case suggests that reconstruction of the sagittal alignment of the medial column and hallux through a combination of osteotomy and soft tissue intervention could be an optional treatment for interphalangeal hyperextension.

Hypoxia-inducible factor-1 alpha maintains mouse articular cartilage through suppression of NF-κB signaling.

HIF-1α, an essential transcription factor under hypoxic condition, is indispensable for chondrocytes during skeletal development but its expression and roles in articular chondrocytes are yet to be revealed. We examined HIF-1α protein expression and the hypoxic condition during mouse osteoarthritis (OA) development using state of the art hypoxic probes and found that its expression decreased as OA progressed, coinciding with the change in hypoxic conditions in articular cartilage. Gain- and loss-of-function of HIF-1α in cell culture experiments showed that HIF-1α suppressed catabolic genes such as Mmp13 and Hif2a. We confirmed these anticatabolic effects by measuring glycosaminoglycan release from wild type and conditional knock-out mice femoral heads cultured ex vivo. We went on to surgically induce OA in mice with chondrocyte-specific deletion of Hif1a and found that the development of OA was exacerbated. Increased expression of catabolic factors and activation of NF-κB signalling was clearly evident in the knock-out mice. By microarray analysis, C1qtnf3 was identified as a downstream molecule of HIF-1α, and experiments showed it exerted anti-catabolic effects through suppression of NF-κB. We conclude that HIF-1α has an anti-catabolic function in the maintenance of articular cartilage through suppression of NF-κB signalling.

Alleviation of murine osteoarthritis by deletion of the focal adhesion mechanosensitive adapter, Hic-5.

Excessive mechanical stress is a major cause of knee osteoarthritis. However, the mechanism by which the mechanical stress begets osteoarthritis development remains elusive. Hydrogen peroxide-inducible clone-5 (Hic-5; TGFß1i1), a TGF-ß inducible focal adhesion adaptor, has previously been reported as a mediator of mechanotransduction. In this study, we analyzed the in vivo function of Hic-5 in development of osteoarthritis, and found that mice lacking Hic-5 showed a significant reduction in development of osteoarthritis in the knee. Furthermore, we found reduced expression of catabolic genes, such as metalloproteinase-13 and a disintegrin and metalloproteinase with thrombospondin type 1 motif 5 in osteoarthritic lesions in mice lacking Hic-5. During osteoarthritis development, Hic-5 is detected in chondrocytes of articular cartilage. To investigate the role of Hic-5 in chondrocytes, we isolated chondrocytes from articular cartilage of wild type and Hic-5-deficient mice. In these primary cultured chondrocytes, Hic-5 deficiency resulted in suppression of catabolic gene expression induced by osteoarthritis-related cytokines such as tumor necrosis factor α and interleukin 1ß. Furthermore, Hic-5 deficiency in chondrocytes suppressed catabolic gene expression induced by mechanical stress. Revealing the regulation of chondrocyte catabolism by Hic-5 contributes to understanding the pathophysiology of osteoarthritis induced by mechanical stress.

Range of Normal and Abnormal Syndesmotic Measurements Using Weightbearing CT.

BACKGROUND: Early recognition of syndesmotic instability is critical for optimizing clinical outcome. Injuries causing a more subtle instability, however, can be difficult to diagnose. The purpose of this study was to evaluate both distal tibiofibular articulations using weightbearing computed tomography (CT) in patients with known syndesmotic instability, thereafter comparing findings between the injured and uninjured sides. We also aimed to define the range of normal measurement variation among patients without syndesmotic injury. METHODS: Patients with unilateral syndesmotic instability requiring operative fixation (n = 12) underwent preoperative bilateral ankle weightbearing CT. A separate cohort of patients without ankle injury who also underwent bilateral ankle weightbearing CT were included as comparative controls (n = 24). For each weightbearing CT, a series of 7 axial plane tibiofibular joint measurements, including 1 angular measurement, were utilized to evaluate parameters of the syndesmotic anatomy at a level 1 cm above the tibial plafond. Values were recorded by 2 independent observers to assess for interobserver reliability. RESULTS: Among those with unilateral syndesmotic instability, values differed between the injured and uninjured sides in 4 of the 7 measurements performed including the syndesmotic area: direct anterior, middle, and posterior differences, and sagittal translation (P < .001, < .001, < .001, and < .001, respectively). In the control population without ankle injury, no differences were identified between any of the bilateral measurements (P value range, .172-.961). CONCLUSION: This study highlights the ability of weightbearing CT to effectively differentiate syndesmotic diastasis among patients with surgically confirmed syndesmotic instability from those without syndesmotic instability. It underscores the substantial utility and importance of using the contralateral, uninjured side as a valid internal control whenever the need for confirming potential syndesmotic instability arises. Prospective studies are necessary to fully understand the accuracy of weightbearing CT in diagnosing occult syndesmotic instability among patients for whom the diagnosis remains in question. LEVEL OF EVIDENCE: Level III, comparative diagnostic study.