Background. Weightbearing computed tomography scans allow for better understanding of foot alignment in patients with Progressive Collapsing Foot Deformity. However, soft tissue integrity cannot be assessed via WBCT. As performing both WBCT and magnetic resonance imaging is not cost effective, we aimed to assess whether there is an association between specific WBCT and MRI findings. Methods. A cohort of 24 patients of various stages of PCFD (mean age 51±18 years) underwent WBCT scans and MRI. In addition to signs of sinus tarsi impingement, four three-dimensional measurements (talo-calcaneal overlap, talo-navicular coverage, Meary's angle axial/lateral) were obtained using a post processing software (DISIOR 2.1, Finland) on the WBCT datasets. Sinus tarsi obliteration, spring ligament complex and tibiospring ligament integrity, as well as tibialis posterior tendon degeneration were evaluated with MRI. Statistical analysis was performed for significant (P<0.05) correlation between findings. Results. None of the assessed 3D measurements correlated with spring ligament complex or tibiospring ligament tears. Age, body mass index, and TCO were associated with tibialis posterior tendon tears. 75% of patients with sinus tarsi impingement on WBCT also showed signs of sinus tarsi obliteration on MRI. Of the assessed parameters, only age and BMI were associated with sinus tarsi obliteration diagnosed on MRI, while the assessed WBCT based 3D measurements were, with the exception of MA axial, associated with sinus tarsi impingement. Conclusion. While WBCT reflects foot alignment and indicates signs of osseous impingement in PCFD patients, the association between WBCT based 3D measurements and ligament or tendon tears in MRI is limited. Partial or complete tears of the tibialis posterior tendon were only detectable in comparably older and overweight PCFD patients with an increased TCO. WBCT does not replace MRI in diagnostic value. Both imaging options add important information and may impact decision-making in the treatment of PCFD patients

Introduction. Corrective fusion for the unstable deformed hind foot in Charcot Neuroarthropathy (CN) is quite challenging and is best done in tertiary centres under the supervision of multidisciplinary teams. Patients and methods. We present our results with a series of 42 hind foot deformity corrections in 40 patients from a tertiary level teaching hospital in the United Kingdom. The mean patient age was 59 (33–82). 16 patients had type1 diabetes mellitus, 20 had type 2 diabetes and 4 were non-diabetic. 18 patients had chronic ulceration. 17 patients were ASA 2 and 23 were ASA grade 3. All patients had acute single stage correction and Trigen hind foot nail fusion performed through a standard technique by the senior author and managed peri-operatively by the multidisciplinary team. Our outcome measures were limb salvage, deformity correction, ulcer healing, weight bearing in surgical shoes and return to activities of daily living (ADL). Results. At a mean follow up of 37 months (7–79) we achieved 100% limb salvage initially and 97% healing of arthrodesis. One patient with persisting non-union has been offered amputation. Deformity correction was achieved in 100% and ulcer healing in 89%. 72.5% patients are able to mobilize and manage independent ADL. There were 11 patients with one or more complications including metal failure, infection and ulcer reactivation. We performed nine repeat procedures including one revision fusion and one vascular procedure. Conclusion. Single stage corrective fusion for hind foot deformity in CN is an effective procedure when delivered by a skilled multidisciplinary team

Aims. In our unit, we adopt a two-stage surgical reconstruction approach using internal fixation for the management of infected Charcot foot deformity. We evaluate our experience with this functional limb salvage method. Methods. We conducted a retrospective analysis of prospectively collected data of all patients with infected Charcot foot deformity who underwent two-stage reconstruction with internal fixation between July 2011 and November 2019, with a minimum of 12 months’ follow-up. Results. We identified 23 feet in 22 patients with a mean age of 56.7 years (33 to 70). The mean postoperative follow-up period was 44.7 months (14 to 99). Limb salvage was achieved in all patients. At one-year follow-up, all ulcers have healed and independent full weightbearing mobilization was achieved in all but one patient. Seven patients developed new mechanical skin breakdown; all went on to heal following further interventions. Fusion of the hindfoot was achieved in 15 of 18 feet (83.3%). Midfoot fusion was achieved in nine of 15 patients (60%) and six had stable and painless fibrous nonunion. Hardware failure occurred in five feet, all with broken dorsomedial locking plate. Six patients required further surgery, two underwent revision surgery for infected nonunion, two for removal of metalwork and exostectomy, and two for dynamization of the hindfoot nail. Conclusion. Two-stage reconstruction of the infected and deformed Charcot foot using internal fixation and following the principle of ‘long-segment, rigid and durable internal fixation, with optimal bone opposition and local antibiotic elusion’ is a good form of treatment provided a multidisciplinary care plan is delivered. Cite this article: Bone Joint J 2021;103-B(10):1611–1618

Introduction. Pes cavovarus is a foot deformity that can be idiopathic (I-PC) or acquired secondary to other pathology. Charcot-Marie-Tooth disease (CMT) is the most common adult cause for acquired pes cavovarus deformity (CMT-PC). The foot morphology of these distinct patient groups has not been previously investigated. The aim of this study was to assess if morphological differences exist between CMT-PC, I-PC and normal feet (controls) using weightbearing computed tomography (WBCT). Methods. A retrospective analysis of WBCT scans performed between May 2013 and June 2017 was undertaken. WBCT scans from 17 CMT-PC, 17 I-PC and 17 healthy normally-aligned control feet (age-, side-, sex- and body mass index-matched) identified from a prospectively collected database, were analysed. Eight 2-dimensional (2D) and three 3-dimensional (3D) measurements were undertaken for each foot and mean values in the three groups were compared using one-way ANOVA with the Bonferroni correction. Results. Significant differences were observed between CMT-PC or I-PC and controls (p< 0.05). Two-dimensional measurements were similar in CMT-PC and I-PC, except for forefoot arch angle (p= 0.04). 3D measurements (foot and ankle offset, calcaneal offset and hindfoot alignment angle) demonstrated that CMT-PC exhibited more severe hindfoot varus malalignment than I-PC (p= 0.03, 0.04 and 0.02 respectively). Discussion. CMT-related cavovarus and idiopathic cavovarus feet are morphologically different from healthy feet, and CMT feet exhibit increased forefoot supination and hindfoot malalignment compared to idiopathic forms. The use of novel three-dimensional analysis may help highlight subtle structural differences in patients with similar foot morphology but aetiologically different pathology

Introduction. Surgical reconstruction of Charcot joint deformity is increasingly being offered to patients. In our centre a hybrid type fixation technique is utilised: internal and external fixation. This combined fixation has better wound management and earlier mobilisation in this deconditioned patient group. The aim of this study was to assess clinical, radiological and patient reported outcomes for all patients who underwent this hybrid technique. Methods. This is a prospective observational case series of all patients who underwent surgical reconstruction of Charcot foot deformity in a single centre between June 2017 and June 2023. Patient demographics, smoking status, diabetic control and BMI were recorded. Outcomes were determined from case notes and included clinical outcomes (complications, return to theatre, amputation and mortality) radiological outcomes and patient reported outcomes. The follow up period was 1–7 years post operatively. Results. 42 reconstructions were included. At the time of surgery the mean age was 59.1 years (29 – 91 years), average HbA1c was 65.2 (33–103); this did not correlate with return to theatre rate. 4 procedures were internal fixation alone (9.5%), 3 external fixation alone (7.1%) and 35 were combined fixation (83.3%). At most recent follow up 7 patients were deceased (16.7%), 2 patients had ipsilateral amputations, 2 had contralateral amputations. 11 patients had issues with recurrent ulcerations. Excluding refreshing of frames and operations on the contralateral side, 17 patients (40%) returned to theatre. We aim to present a detailed analysis of the rate of post-operative complications, return to theatre, radiographic outcomes and patient reported outcomes. Conclusion. This is the largest UK based case series of hybrid type Charcot joint reconstructions and shows that hybrid fixation is a viable option for patients undergoing Charcot joint reconstruction. To best confirm findings and determine which patients have the best post-operative prognosis a larger multi-centre study is required

Tendinopathy can commonly occur around the foot and ankle resulting in isolated rupture, debilitating pain and degenerative foot deformity. The pathophysiology and key cells involved are not fully understood. This is partly because the dense collagen matrix that surrounds relatively few resident cells limits the ability of previous techniques to identify and target those cells of interest. In this study, we apply novel single cell RNA sequencing (CITE-Seq) techniques to healthy and tendinopathic foot/ankle tendons. For the first time we have identified multiple sub-populations of cells in human tendons. These findings challenge the view that there is a single principal tendon cell type and open new avenues for further study. Healthy tendon samples were obtained from patients undergoing tendon transfer procedures; including tibialis posterior and FHL. Diseased tendon samples were obtained during debridement of intractable Achilles and peroneal tendinopathy, and during fusion of degenerative joints. Single cell RNA sequencing with surface proteomic analysis identified 10 sub-populations of human tendon derived cells. These included groups expressing genes associated with fibro-adipogenic progenitors (FAPs) as well as ITGA7+VCAM1- recently described in mouse muscle but, as yet, not human tendon. In addition we have identified previously unrecognised sub-classes of collagen type 1 associated tendon cells. Each sub-class expresses a different set of extra-cellular matrix genes suggesting they each play a unique role in maintaining the structural integrity of normal tendon. Diseased tendon harboured a greater proportion of macrophages and cytotoxic lymphocytes than healthy tendon. This inflammatory response is potentially driven by resident tendon fibroblasts which show increased expression of pro-inflammatory cytokines. Finally, identification of a previously unknown sub-population of cells found predominantly in tendinopathic tissue offers new insight into the underlying pathophysiology. Further work aims to identify novel proteins targets for possible therapeutic pathways

Background. The complex deformities in cavovarus feet may be difficult to assess and understand. Weight-bearing CT (WBCT) is increasingly used to evaluate complex deformities. However, the bone axes may be difficult to calculate in the setting of severe deformity. Computer-assisted 3D-axis calculation is a novel approach that may allow for more accurate assessment of foot alignment / deformity. The aim of this study was to assess differences in measurements done manually on 2D slices of WBCT versus 3D computer models in normal and cavus feet. Methods. We retrospectively analyzed WBCT scans from 16 normal and 16 cavus feet in patients with Charcot-Marie Tooth. Eight measurements were assessed: Talus-1. st. metatarsal angle (axial plane), Forefoot arch angle (coronal plane), and Meary's angle, calcaneal pitch, cuneiform to floor, cuneiform to skin, navicular to floor and navicular to skin distance (sagittal plane). 2D measurements were performed manually and 3D measurements were performed using specialised software (BoneLogic, DISIOR). Results. There was no significant difference in the measured variables (2D manual versus 3D automated) in normal feet. In the cavus group, 3D assessment calculated increased values for the sagittal angles: Meary's 7.3 degrees greater (p = 0.004), calcaneal pitch 2.4 degrees greater (p = 0.011)), and lower values for the axial talus-1. st. MT angle, 10.6 degrees less (p = 0.001). Conclusion. There were no significant differences in the normal group. This suggests 3D automated techniques can reliably assess the alignment of bony axes. However, the 3D axis calculations suggest there may be greater sagittal and lesser axial deformity in cavus feet than measured by 2D techniques. This discrepancy may be on account of the rotation seen in cavovarus feet, which may not be readily assessed manually. 3D automated measurements may therefore have a role in better assessing and classifying the cavus foot which may ultimately help inform treatment algorithms

Introduction. Stress fractures in the foot are common; the common practice is to look for any factor in the history or for any foot deformity that could cause the fracture. Once found, it is common to treat the fractures without further investigations. The aim of this study is to assess if we are missing any underlying metabolic disorder associated with such injury. Materials and methods. We studied 34 sequential cases referred for chronic foot pain. Stress fractures were confirmed either by classic x-ray's features or MRI. Clinical examination and further tests were performed for Vitamin D levels, Thyroid function, PTH, DEXA scan, Biochemical and bone profile. All stress fractures were treated conservatively. Results. Mean age was 50 (13–72) (22 Females, 9 Males), 29 patients were fit and healthy ASA 1, 5 cases were ASA 2. 12 cases presented with a precipitating event. 14 cases had a minor foot deformity (such as hallux valgus of minor pes planus). mean BMI 27.6. The blood tests newly diagnosed: 17 Vitamin D deficiencies cases, 2 hyperparathyroidism cases, one case of Cushing's Syndrome secondary to adrenal adenoma and one case of delay in puberty in addition to 3 osteoporosis cases. All fractures responded to conservative means of treatment and none needed surgical interventions. Discussion. The study shows that the incidence of endocrinological disorders is patients presenting with stress fractures is much higher than the incidence in the general population; for example the incidence of Cushing's syndrome is 1 per 130000 individuals while in our series was 1 per 34. This study raises the question if all patients presetting with stress fractures should be investigated for endocrinological disorders

Rocker bottom deformity may occur during the conservative treatment of idiopathic congenital clubfoot. Between 1975 and 1996, we treated 715 patients (1120 clubfeet) conservatively. A total of 23 patients (36 feet; 3.2%) developed a rocker bottom deformity. It is these patients that we have studied. The pathoanatomy of the rocker bottom deformity is characterised by a plantar convexity appearing between three and six months of age with the hindfoot equinus position remaining constant. The convexity initially involves the medial column, radiologically identified by the talo-first metatarsal angle and secondly by the lateral column, revealed radiologically as the calcaneo-fifth metatarsal angle. The apex of the deformity is usually at the midtrasal with a dorsal calcaneocuboid subluxation. Ideal management of clubfoot deformity should avoid this complication, with adequate manipulation and splinting and early Achilles’ percutaneous tenotomy if plantar convexity occurs. Adequate soft-tissue release provides satisfactory correction for rocker bottom deformity. However, this deformity requires more extensive and complex procedures than the standard surgical treatment of clubfoot. The need for lateral radiographs to ensure that the rocker bottom deformity is recognised early, is demonstrated

Aims

The Vantage Total Ankle System is a fourth-generation low-profile fixed-bearing implant that has been available since 2016. We aimed to describe our early experience with this implant.

Aims

The Chopart joint complex is a joint between the midfoot and hindfoot. The static and dynamic support system of the joint is critical for maintaining the medial longitudinal arch of the foot. Any dysfunction leads to progressive collapsing flatfoot deformity (PCFD). Often, the tibialis posterior is the primary cause; however, contrary views have also been expressed. The present investigation intends to explore the comprehensive anatomy of the support system of the Chopart joint complex to gain insight into the cause of PCFD.

Introduction. Metatarsus adductus (MA) increases the risk of recurrence following surgery for hallux valgus (HV). The goal of this study was to analyze patients with severe MA and identify clinical/surgical factors that are associated with a lower rate of recurrent deformity. Methods. 587 patients underwent correction of HV deformity. The rate of recurrence of HV was 15% (63 out of 414 patients) in patients without MA (MA angle < 20°) and 29.6% (50 out of 173 patients) in patients with MA. 19 patients with severe MA (>31°) were identified; 8 of 19 had associated tarsometatarsal arthritis, and two patients had a skew foot deformity. Ten patients had severe valgus lesser toe deformities. Clinical information collected included associated diagnoses, the presence of arthritis of the tarsometatarsal joints, the presence and degree of lesser toe valgus deformities and surgical procedures performed. Radiographic recurrence was defined as a postoperative HVA > 20°. Results. 9/19 patients were treated with a modified Lapidus procedure and 10 patients underwent a distal first metatarsal osteotomy. Of the 9 patients who were treated with a modified Lapidus procedure, 6 patients underwent simultaneous realignment lesser metatarsal osteotomy or arthrodesis of the 2. nd. /3. rd. TMT joints. 1/9 of these patients had radiographic recurrence of deformity. Of the 10 patients who underwent a distal first metatarsal osteotomy without realignment proximal osteotomy or arthrodesis, 5 had recurrence of deformity. Of the 11 patients with severe valgus lesser toe deformity, those who were treated with simultaneous additional distal lesser metatarsal osteotomies, did not have recurrence of hallux valgus. Conclusion. The use of a modified Lapidus procedure led to a lower rate of HV deformity recurrence in comparison to isolated distal first metatarsal osteotomies. Treatment of lesser toe deformity with distal osteotomy should be included as part of the treatment algorithm

Introduction. In 1927, Lambrinudi described a variant triple fusion for the treatment of paralytic “drop foot”. This involved closing wedge osteotomies and fusion to correct the deformities predominantly caused by Polio. The eradication of Polio has seen a shift in its use to the correction of other complex hind foot deformities. The technique has relevance in modern Orthopaedics for other neurological and degenerate conditions. There have been few published series of this technique since 1927. We describe a series of 14 complex corrective triple arthrodeses to illustrate the power of Lambrinudi's concepts. We believe Lambrinudi's original description has relevance in terms of modern day complex hindfoot deformity correction

Introduction:. The purpose of this study was to elucidate the specific radiographic effects that the Cotton osteotomy confers when used in combination with other reconstructive procedures in the management of the flexible flat foot deformity. Methods:. Between 2002–2013, 198 Cotton osteotomies were retrospectively identified following IRB approval. 131 were excluded on the basis of ipsilateral mid/hindfoot arthrodesis, inadequate radiographs or being less than 18yrs old at time of surgery. Parameters including the articular surface angles of the hindfoot/forefoot, Meary's angle and a newly defined Medial Arch Sag Angle (MASA) were recorded. A matched group of patients who did not undergo a Cotton osteotomy but who underwent similar hindfoot reconstructive procedures served as historic controls. Results:. 67 Cotton osteotomies in 59 patients with a mean age of 45 years (range, 18–80) were evaluated. Concomitant procedures included combinations of tibialis posterior tendon (PTT) reconstruction, Evans lateral column lengthening, medial displacement calcaneal osteotomy (MDCO). In all patients who underwent a Cotton osteotomy, there were statistically significant improvements in the articular surface angles along the medial side of the foot (p < 0.05). Improvement in arch height was also found to be statistically significant (p < 0.05). In comparison to matched controls, the Cotton osteotomy did not improve Meary's angle but provided an additional 11.21° of MASA correction (p < 0.05) when used in in conjunction with the Evans procedure and PTT reconstruction. A similar trend was seen with MDCO and PTT reconstruction. Discussion:. This study confirms the Cotton osteotomy is a powerful surgical adjunct in flatfoot reconstruction and quantifies the additional 11.21° of MASA correction it provides when the Cotton osteotomy is added to a calcaneal osteotomy and PTT reconstruction. This has relevance as an alternative for selection of a medial column stabilization procedure, which is joint sparing

Background:. Calcaneal osteotomy is an established technique in correcting hind foot deformity. Patients have traditionally received an open osteotomy through Atkins lateral approach. In order to reduce the rate of wound complications associated with the Atkins approach, a minimally invasive surgical (MIS) technique has been adopted since 2011. This uses a low-speed, high-torque burr to perform the same osteotomy under radiographic guidance. The results of the new MIS technique, including post-operative complication rates, are compared to the standard open approach. Methods:. The safety of the new MIS technique was investigated by conducting a case controlled study on all patients who underwent displacement calcaneal osteotomy at the Nuffield Orthopaedic Centre, Oxford from 2008 to 2014. The primary outcome measure was 30 day post-operative complication rate. Secondary outcome measures included operating time, duration of stay, fusion rates and amount of displacement achieved. Results:. 82 patients underwent calcaneal osteotomy as part of their corrective surgery; 50 patients in the Open approach group and 32 patients in MIS group. The average age at the time of surgery was 47.7 years (range 16–77) for the Open group and 48.5 (range 21–77) in the MIS group. A mean calcaneal displacement of 8.0mm (s.d. 1.32, 7 to 11 mm) and 8.33mm (s.d.1.53, 6 to 10 mm) was achieved through the MIS and open approaches respectively. There were significantly fewer wound complications in the MIS group (6.25%) compared to the Open group (28%, P=0.021) and the MIS group was associated with significantly lower rates of wound infection (3% versus 20%, P = 0.043). Three patients in the Open group experienced sural peripheral neuropathy. Conclusions:. MIS calcaneal osteotomy was found to be a safe technique. It was as effective as calcaneal osteotomy performed through an open lateral approach but was associated with significantly fewer wound complications and fewer nerve complications

Introduction. Longstanding complex muliplanar foot deformities represent a significant challenge. The traditional surgical techniques involve excessive dissection and excision of large bony wedges or modifications of the triple fusion to correct the deformity. The majority of the reports in the literature present collective data on different deformity patterns and also mix paediatric and adult patients, even with multiple correction techniques. The aim of this study was to evaluate the clinical, radiological and functional outcomes of the gradual correction of a single common deformity pattern of equino-cavo-varus using a single correction technique of the V-osteotomy and the Ilizarov frame. Material and methods. We present prospectively collected data on 40 feet in 35 adult patients with stiff longstanding equino-cavo-varus deformity. All patients had a V-osteotomy and gradual correction using an Ilizarov frame, with a mean follow-up of 20 months. We collected the American Orthopaedic Foot and Ankle Scocity score (AOFAS), the Foot and Ankle Disability Index (FADI) and a Visual Analogue Pain score (VAS) for all ptients preoperatively and between 1 and 2 years following frame removal. Results. In 33 patients (38 feet) a stable plantigrade foot was achieved with significant improvement in the gait and the foot alignment. The mean equinus, heel varus and metatarsus adductus improved significantly as measured on x-rays. The mean AOFAS score improved from 38.2 to 73.2, the mean FADI improved from 51.1 to 70.6 and the mean VAS improved from 4.5 to 0.5. Pin-site infection was encountered in 7 feet, premature consolidation in 2 feet and undercorrection in 4 feet. In 2 patients the correction had to be stopped. Conclusion. The results of this report on a single deformity pattern of equino-cavo-varus support the use of this technique for the management of these challenging cases, as a safe, versatile and powerful tool with predictable outcome

This study assessed if transfer of the extensor hallucis longus is a valid alternative treatment to split transfer of the tibialis anterior tendon in adult hemiplegic patients without overactivity of the tibialis anterior. One group of 15 patients had overactivity of tibialis anterior in the swing phase, and underwent the split transfer. A further group of 14 patients had no overactivity of tibialis anterior, and underwent transfer of extensor hallucis longus. All patients had lengthening of the tendo Achillis and tenotomies of the toe flexors. All were evaluated clinically and by three-dimensional gait analysis pre- and at one year after surgery. At this time both groups showed significant reduction of disability in walking. Gait speed, stride length and paretic propulsion had improved significantly in both groups. Dorsiflexion in the swing phase, the step length of the healthy limb and the step width improved in both groups, but only reached statistical significance in the patients with transfer of the extensor hallucis longus. There were no differences between the groups at one year after operation. When combined with lengthening of the tendo Achillis, transfer of the extensor hallucis longus can be a valid alternative to split transfer of the tibialis anterior tendon to correct equinovarus foot deformity in patients without overactivity of tibialis anterior

Aims

To assess the characteristic clinical features, management, and outcome of patients who present to orthopaedic surgeons with functional dystonia affecting the foot and ankle.

We investigated 60 patients (89 feet) with a mean age of 64 years (61 to 67) treated for congenital clubfoot deformity, using standardised weight-bearing radiographs of both feet and ankles together with a functional evaluation. Talocalcaneal and talonavicular relationships were measured and the degree of osteo-arthritic change in the ankle and talonavicular joints was assessed. The functional results were evaluated using a modified Laaveg-Ponseti score. The talocalcaneal (TC) angles in the clubfeet were significantly lower in both anteroposterior (AP) and lateral projections than in the unaffected feet (p < 0.001 for both views). There was significant medial subluxation of the navicular in the clubfeet compared with the unaffected feet (p < 0.001). Severe osteoarthritis in the ankle joint was seen in seven feet (8%) and in the talonavicular joint in 11 feet (12%). The functional result was excellent or good (≥ 80 points) in 29 patients (48%), and fair or poor (< 80 points) in 31 patients (52%). Patients who had undergone few (0 to 1) surgical procedures had better functional outcomes than those who had undergone two or more procedures (p < 0.001). There was a significant correlation between the functional result and the degree of medial subluxation of the navicular (p < 0.001, r. 2 . = 0.164), the talocalcaneal angle on AP projection (p < 0.02, r2 = 0.025) and extent of osteoarthritis in the ankle joint (p < 0.001). We conclude that poor functional outcome in patients with congenital clubfoot occurs more frequently in those with medial displacement of the navicular, osteoarthritis of the talonavicular and ankle joints, and a low talocalcaneal angle on the AP projection, and in patients who have undergone two or more surgical procedures. However, the ankle joint in these patients appeared relatively resistant to the development of osteoarthritis

Medial Displacement Osteotomy (MDO) of the os calcis is used to correct the hind foot valgus in a flat foot deformity. Screw fixation is commonly used although contemporary locking plate systems are now available. This study tested the hypothesis that a 10mm MDO would support a higher load to failure with a locked step plate than with a single cannulated screw. Materials and Methods. Eight pairs of embalmed cadaveric limbs harvested 10cm below the knee joint were axially loaded using a mechanical testing rig. Two pairs served as non-operated controls loaded to 4500N. The remaining limbs in pairs underwent a 10mm MDO of the os calcis and were stabilised with a locked step plate or a 7mm cannulated compression screw. One pair was loaded to 1600N (twice body weight) as a pilot study and the remaining 5 pairs were loaded to failure up to 4500N. The force-displacement curve and maximum force were correlated with observations of the mechanism of failure. Results. In one pair of control limbs, failure occurred with fractures through both os calcis bones, whilst the other pair did not undergo mechanical failure to 4500N. In the pilot osteotomy, the plate did not fail whilst loss of fixation with the screw was observed below 1600N. For the remaining five pairs, the median (with 95% Confidence Intervals) of the maximum force under load to failure were 1778.81N (1099.39 – 2311.66) and 826.13N (287.52 – 1606.67) for the plate and screw respectively (Wilcoxon Signed Rank test p=0.043). In those with screw fixation loaded to 4500N, the tuberosity fragment consistently failed by rotation and angulation into varus. Conclusion. In this model of load to failure with a medial displacement os calcis osteotomy, a locked step plate supported a significantly higher maximum force than a single large cannulated screw