The Reliability and Validity of Wearable Inertial Sensors Coupled with the Microsoft Kinect to Measure Shoulder Range-of-Motion.

BACKGROUND: Objective assessment of shoulder joint active range of motion (AROM) is critical to monitor patient progress after conservative or surgical intervention. Advancements in miniature devices have led researchers to validate inertial sensors to capture human movement. This study investigated the construct validity as well as intra- and inter-rater reliability of active shoulder mobility measurements using a coupled system of inertial sensors and the Microsoft Kinect (HumanTrak). METHODS: 50 healthy participants with no history of shoulder pathology were tested bilaterally for fixed and free ROM: (1) shoulder flexion, and (2) abduction using HumanTrak and goniometry. The repeat testing of the standardised protocol was completed after seven days by two physiotherapists. RESULTS: All HumanTrak shoulder movements demonstrated adequate reliability (intra-class correlation (ICC) ≥ 0.70). HumanTrak demonstrated higher intra-rater reliability (ICCs: 0.93 and 0.85) than goniometry (ICCs: 0.75 and 0.53) for measuring free shoulder flexion and abduction AROM, respectively. Similarly, HumanTrak demonstrated higher intra-rater reliability (ICCs: 0.81 and 0.94) than goniometry (ICCs: 0.70 and 0.93) for fixed flexion and abduction AROM, respectively. Construct validity between HumanTrak and goniometry was adequate except for free abduction. The differences between raters were predominately acceptable and below ±10°. CONCLUSIONS: These results indicated that the HumanTrak system is an objective, valid and reliable way to assess and track shoulder ROM.

Pedicle screw pull-out testing in polyurethane foam blocks: Effect of block orientation and density.

Synthetic bone models such as polyurethane (PU) foam are a well-established substitute to cadaveric bone for screw pull-out testing; however, little attention has been given to the effect of PU foam anisotropy on orthopaedic implant testing. Compressive and screw pull-out performance in three PU foam densities; 0.16 g/cm3 (PCF 10), 0.32 g/cm3 (PCF 20) and 0.64 g/cm3 (PCF 40) were performed in each of the X, Y or Z orientations. The maximum compressive force, stiffness in the linear region, maximum stress and modulus were determined for all compression tests. Pedicle screws were inserted and pulled out axially to determine maximum pull-out force, energy to failure and stiffness. One-way ANOVA and post hoc tests were used to compare outcome variables between PU foam densities and orientations, respectively. Compression tests demonstrated the maximum force was significantly different between all orientations for PCF 20 (X, Y and Z) while stiffness and maximum stress were different between X versus Y and X versus Z. Maximum pull-out force was significantly different between all orientations for PCF 10 foam. No significant differences were noted for other foam densities. There is potential for screw pull-out testing results to be significantly affected by orientation in lower density PU foams. It is recommended that a single, known orientation of the PU foam block be used for experimental testing.

Bone ongrowth and mechanical fixation of implants in cortical and cancellous bone.

BACKGROUND: What is the right surface for an implant to achieve biological fixation? Surface technologies can play important roles in encouraging interactions between the implant surface and the host bone to achieve osseointegration. Preclinical animal models provide important insight into in vivo performance related to bone ongrowth and implant fixation. METHODS: A large animal model was used to compare the in vivo response of HA and plasma-sprayed titanium coatings in a well-reported adult ovine model to evaluate bone ongrowth in terms of mechanical properties in cortical sites, and histology and histomorphometry in cortical and cancellous sites at 4 and 12 weeks. RESULTS: Titanium plasma-sprayed surfaces outperformed the HA-coated samples in push-out testing in cortical sites while both surfaces supported new bone ongrowth and remodeling in cortical and cancellous sites. CONCLUSIONS: While both HA and Ti plasma provided an osteoconductive surface for bone ongrowth, the Ti plasma provided a more robust bone-implant interface that ideally would be required for load transfer and implant stability in the longer term.

Three-Dimensional Morphometric Analysis of Lumbar Vertebral End Plate Anatomy.

BACKGROUND: Information on the three-dimensional (3D) shape of vertebral end plates is lacking. Previous studies have analyzed two-dimensional shape; however, 3D data are important because they may help improve our understanding of how differences in shape are related to age, gender, race, size, and other parameters, which may subsequently help improve device design for interbody prosthesis. OBJECTIVE: To study the 3D shape of lumbar vertebral end plates from normal adult lumbar spines and correlate them with age, gender, spinal/end plate level, end plate surface area, concave depth, and size. METHODS: An in vivo analysis was undertaken of lumbar vertebral end plate 3D shape. A total of 136 patients' computed tomography scans were used to create 3D models of the lumbar spine for each patient, which were subsequently analyzed. RESULTS: The shape of the superior end plates is different compared with inferior end plates. Across the lumbar spine (L1-S1), the shape of inferior end plates is similar; however, the shape of the superior end plate varies between spinal levels significantly. There was no clear relationship between age and principal component (PC) shapes but there was a strong correlation between end plate concave depth and end plate PC shape scores. CONCLUSIONS: Future interbody (disc replacement and fusion) device designs could use the findings that inferior end plate shape is similar throughout the length of the lumbar spine, whereas superior end plate shape changes. Further, future implants could be level-specific because the present study shows that end plate shape varies through the length of the lumbar spine.

Posterolateral spinal fusion in a rabbit model using a collagen-mineral composite bone graft substitute.

Choosing the appropriate graft material to participate in the healing process in posterolateral spinal fusion continues to be a challenge. Combining synthetic graft materials with bone marrow aspirate (BMA) and autograft is a reasonable treatment option for surgeons to potentially reduce or replace the need for autograft. FormaGraft, a bone graft material comprising 12% bovine-derived collagen and 88% ceramic in the form of hydroxyapatite (HAp) and beta tricalcium phosphate (beta-TCP) was evaluated in three possible treatment modalities for posterior spinal fusion in a standard rabbit model. These three treatment groups were FormaGraft alone, FormaGraft soaked in autogenous BMA, and FormaGraft with BMA and iliac crest autograft. No statistically demonstrable benefits or adverse effects of the addition of BMA were found in the current study based on macroscopic, radiology or mechanical data. This may reflect, in part, the good to excellent results of the collagen HA/TCP composite material alone in a well healing bony bed. Histology did, however, reveal a benefit with the use of BMA. Combining FormaGraft with autograft and BMA achieved results equivalent to autograft alone. The mineral and organic nature of the material provided a material that facilitated fusion between the transverse processes in a standard preclinical posterolateral fusion model.

Corrosion of 3D-Printed Orthopaedic Implant Materials.

3D-printing technologies such as electron beam melting (EBM) have allowed for patient-specific orthopaedic implants, however differences generated from the fabrication process may alter the corrosion properties of Ti6Al4V implants. This study evaluated the corrosion characteristics of EBM-fabricated Ti6Al4V, alongside any linked microstructural and surface changes. EBM-fabricated Ti6Al4V and wrought Ti6Al4V specimens (n = 10 per group) underwent microstructural and surface characterisation before and after corrosion testing. Cyclic potentiodynamic polarisation of specimens was conducted in accordance with ASTM Standard F2129-17. The degree of corrosion damage was subsequently assessed via qualitative and quantitative measures. EBM-fabricated Ti6Al4V demonstrated a higher proportion of ß phases and greater surface roughness, compared to wrought Ti6Al4V. Significant differences were observed for all corrosion parameters between the two groups. The lower breakdown potentials (Eb) for EBM-fabricated Ti6Al4V (2.035 V), compared to wrought Ti6Al4V (3.667 V), indicate a lower resistance to pitting corrosion. A greater resultant spread, and severity of corrosion damage was noted on wrought Ti6Al4V. An inferior in vitro corrosion resistance was observed for EBM-fabricated Ti6Al4V. Without post-processing, the rougher surface and differences in microstructure are likely to contribute to this. This suggests potential clinical implications upon in vivo implantation, although corrosion measures remain above recommended minimums.

The in vivo response to a novel Ti coating compared with polyether ether ketone: evaluation of the periphery and inner surfaces of an implant.

BACKGROUND CONTEXT: Increasing bone ongrowth and ingrowth of polyether ether ketone (PEEK) interbody fusion devices has the potential to improve clinical outcomes. PURPOSE: This study evaluated the in vivo response of promoting new bone growth and bone apposition with NanoMetalene (NM) compared with PEEK alone in a cancellous implantation site with an empty aperture. STUDY DESIGN: This is a randomized control animal study. METHODS: Implants and funding for this study were provided by SeaSpine (60,000 USD). Cylindrical dowels with two apertures were prepared as PEEK with a sub-micron layer of the titanium (NM). The titanium coating was applied over the entire implant (Group 1) or just the apertures (Group 2). Polyether ether ketone implants with no coating served as controls (Group 3). Implants were placed in the cancellous bone of the distal femur or proximal tibia with no graft material placed in the apertures in eight adult sheep. Bone ongrowth to the surface of the implant and ingrowth into the apertures was assessed at 4 and 8 weeks after surgery with micro-computed tomography (CT) and undecalcified histology. RESULTS: The apertures in the implants were notably empty in the PEEK group at 4 and 8 weeks. In contrast, new bone formation into the apertures was found in samples coated with NM even though no graft material was placed into the defect. The bone growing into the aperture tracked along the titanium layer. Apertures with the titanium coating demonstrated significantly more bone by micro-CT qualitative grading compared with PEEK with average bone coverage scores of Group 1 (NM) 1.62±0.89, Group 2 (NM apertures only) 1.62±0.77, and Group 3 (PEEK) 0.43±0.51, respectively, at 4 weeks (p<.01) and Group 1 (NM) 1.79±1.19, Group 2 (NM apertures only) 1.98±1.18, and Group 3 (PEEK) 0.69±0.87, respectively, at 8 weeks (p<.05). The amount of bone in the apertures (ingrowth) quantified using the volumetric data from the micro-CT supported an overall increase in bone volume inside the apertures with the titanium coating compared with PEEK. Histology showed newly formed woven bone tracked along the surface of the titanium in the apertures. The PEEK interface presented the typical nonreactive fibrous tissue inside the apertures at 4 weeks and some focal contact with bone on the outside at 4 weeks and 8 weeks. CONCLUSIONS: Micro-CT and histology demonstrated bone ongrowth to the surfaces coated with NM where the newly formed bone tracked along the thin titanium-coated surfaces. Polyether ether ketone surfaces presented the nonreactive fibrous tissue at the interface as previously reported in preclinical scenarios.

The contribution of the cortical shell to pedicle screw fixation.

BACKGROUND: A pedicle screw insertion technique known as "hubbing" involves the removal of cortical bone around the screw insertion with the aim of improving fixation and decreasing screw loosening. However, the efficacy of this procedure relative to bone density and early loading have not been fully explored. The purpose of this study is to establish the contribution of the cortical layer (hubbing), cancellous density, early loading (toggling) in an idealised model. This is an in vitro laboratory study. METHODS: Synthetic bone blocks with cancellous bulk and a simulated cortical shell were implanted with 6.5 mm pedicle screws. Three key variables were evaluated in this study; density of the simulated bone (10-20 lb/ft3), toggling (±0.5 mm for 10,000 cycles), and the presence or absence of the surrounding cortex (hubbing). Pullout testing after toggling was performed to determine maximum load, stiffness and energy. Results were analyzed to assess interaction and main effects. RESULTS: Removal of the cortex decreased the pullout loads by approximately 1,100 N after toggling. Toggling in the presence of the cortical shell had no effect. However, once the cortical shell is removed damage to the weaker cancellous bone accumulates and further compromises the fixation. CONCLUSIONS: The addition of a cortical layer in the Sawbone model is significant and provides a more realistic model of load sharing. The cortex plays a considerable role in the protection of underlying cancellous bone as well as contributing to initial pullout strength. The results of this study demonstrate a negative synergistic effect when both toggling and hubbing are applied to the weaker bone.

Critical Size Bone Defect Healing Using Collagen-Calcium Phosphate Bone Graft Materials.

The need for bone graft materials to fill bony voids or gaps that are not related to the intrinsic stability of the bone that arise due to trauma, tumors or osteolysis remains a clinically relevant and significant issue. The in vivo response of collagen-tricalcium phosphate bone graft substitutes was evaluated in a critical size cancellous defect model in skeletally mature rabbits. While the materials were chemically virtually identical, new bone formation, implant resorption and local in vivo responses were significantly different. Differences in the in vivo response may be due, in part, collagen source and processing which influences resorption profiles. Continued improvements in processing and manufacturing techniques of collagen-tricalcium phosphate bone graft substitutes can result in osteoconductive materials that support healing of critical size bone defects even in challenging pre-clinical models.

Animal Models for Tendon Repair Experiments: A Comparison of Pig, Sheep and Human Deep Flexor Tendons in Zone II.

BACKGROUND: This laboratory study compared pig, sheep and human deep flexor tendons in regards to their biomechanical comparability. METHODS: To investigate the relevant biomechanical properties for tendon repair experiments, the tendons resistance to cheese-wiring (suture drag/splitting) was assessed. Cheese-wiring of a suture through a tendon is an essential factor for repair gapping and failure in a tendon repair. RESULTS: Biomechanical testing showed that forces required to pulling a uniform suture loop through sheep or pig tendons in Zone II were higher than in human tendons. At time point zero of testing these differences did not reach statistical significance, but differences became more pronounced when forces were measured beyond initial cheese-wiring (2 mm, 5 mm and 10 mm). The stronger resistance to cheese-wiring was more pronounced in the pig tendons. Also regarding size and histology, sheep tendons were more comparable to human tendons than pig tendons. CONCLUSIONS: Differences in tendon bio-properties should be kept in mind when comparing and interpreting the results of laboratory tendon experiments.

Mechanical properties of gamma irradiated morselized bone during compaction.

This study examined the effects of gamma irradiation on the compressive properties of morselized cancellous bone from human femoral heads. Twelve bone samples, mean age of 68 years (range 92-39), were divided into 3 groups (N=12) of varying irradiation level (0, 15 and 25 kGy). Each specimen was compacted in a controlled fashion in steps of 0.5 mm at 0.5 mm/min (up 12 mm). The load and stiffness increased with compaction, but this relationship was not linear. There was no statistical significant difference in the compacting load or stiffness between groups (p>0.05) until the last 1 mm of compaction, where the 25 kGy group were significantly stiffer compared to controls but not different to the 15 kGy group. This may be due to decreased interlocking of bone particles caused by higher irradiation levels resulting in a stiffer graft.

Variations in the trunnion surface topography between different commercially available hip replacement stems.

Modular hip implants allows for the adjustment of leg length, offset, and the ability to remove the head for acetabular exposure during primary and revision surgery. The design of the Morse taper facilitates the intimate contact of the conical trunnion of the femoral stem (male component), with the conical bore of the femoral head (female component). Orthopaedic trunnion tapers are not standardized and vary in length, taper angle, and base dimension. Variations in the design and surface characteristics of the trunnion, will directly reflect on the interface at the taper junction and can influence the likelihood of subsequent wear, corrosion and longevity of the implant. The effect of surface topography of trunnions on commercially available hip stems has not yet been considered as a possible contributing factor in the corrosion observed at taper junctions. In this study we analyzed the surface topography and surface roughness of randomly selected commercially available femoral hip stem trunnions to obtain a greater insight into their surface characteristics.

Structural Failure Mechanisms of Common Flexor Tendon Repairs.

BACKGROUND: This study investigated the exact failure mechanisms of the most commonly used conventional tendon repair techniques. A new method, radiographing repair constructs in antero-posterior and lateral projections before and after tensioning was used. This allowed to precisely analyse failure mechanisms in regards to geometrical changes in all three dimensions. Additionally the biomechanical stability focusing on gapping was tested. METHODS: Sheep fore limb deep flexor tendons were harvested and divided in eight groups of ten tendons. Three common variants of the Kessler repair method and four common 4-strand repair techniques were tested. Additionally a new modification of the Adelaide repair was tested. RESULTS: Biomechanical testing showed no significant differences in gapping for the three tested 2-strand Kessler repair groups. Once a double Kessler or 4-strand Kessler repair was performed the stability of the repair improved significantly. Further significant improvements in biomechanical stability could be achieved by using cross locks in the repair like in the Adelaide repair method. Qualitative analysis using radiographs showed that all Kessler repair variants unfolded via rotations around the transverse suturing component, no matter which variant was used. CONCLUSIONS: Additional to the commonly described constriction of the repair construct, the rotating deformation is the main reason for repair site gapping in Kessler tendon repair methods. The term "locking" in a Kessler repair is misleading. The cruciate repairs tended to loose grip and drag (cheese-wire) through the tendon and therefore lead to gapping. The most stable repair constructs in all three dimensions were the Adelaide repair and its interlocking modification. This is due to the superior anchoring qualities of its cross locks and three dimensional stability.

The immunolocalisation of VEGF in the articular cartilage of sheep mandibular condyles.

INTRODUCTION: Vascular endothelial growth factor (VEGF) has recently been found to be essential for hypertrophic chondrocyte apoptosis and angiogenesis at the growth plate of long bones, indicating a central role in endochondral ossification. VEGF has more recently, also been shown to be expressed in articular cartilage chondrocytes in human osteoarthritic and rheumatoarthritic joints but not healthy adult joints. To investigate the role of VEGF in the fibrocartilage of the temporomandibular joint, this study aimed to document the presence and distribution of VEGF in the condylar articular cartilage of sheep temporomandibular joints. METHODS: Mandibular condyles of the temporomandibular joints of five 18-month old Wether sheep were fixed, decalcified, paraffin embedded and sectioned. The sections were analyzed using immunohistochemistry for VEGF. RESULTS: VEGF was found to be localised predominantly to the proliferative and maturing layers of chondrocytes in the condylar fibrocartilage of the temporomandibular joints. Articular cartilage is an avascular and alymphatic tissue. As such, the localisation of VEGF to the articular cartilage of normal temporomandibular joint condyles suggests a role for VEGF other than angiogenesis. CONCLUSION: VEGF is shown here for the first time to be present in mandibular condylar cartilage, leading us to propose a possible role in non-angiogenic extracellular matrix remodeling.

A sheep model for cancellous bone healing.

Appropriate well-characterized bone defect animal models remain essential for preclinical research. This pilot study demonstrates a relevant animal model for cancellous bone defect healing. Three different defect diameters (8, 11, 14 mm) of fixed depth (25 mm) were compared in both skeletally immature (18-month-old) and aged sheep (5-year-old). In each animal, four defects were surgically created and placed in the cancellous bone of the medial distal femoral and proximal tibial epiphyses bilaterally. Animals were euthanized at 4 weeks post-operatively to assess early healing and any biological response. Defect sites were graded radiographically, and new bone formation quantified using µCT and histomorphometry. Fibrous tissue was found within the central region in most of the defects with woven bone normally forming near the periphery of the defect. Bone volume fraction [bone volume (BV)/TV] significantly decreased with an increasing defect diameter. Actual BV, however, increased with defect diameter. Bone ingrowth was lower for all defect diameters in the aged group. This pilot study proposes that the surgical creation of 11 mm diameter defects in the proximal tibial and distal femoral epiphyses of aged sheep is a suitable large animal model to study early healing of cancellous bone defects. The refined model allows for the placement of four separate bone defects per animal and encourages a reduction in animal numbers required for preclinical research.

The effect of sterilization on the dynamic mechanical properties of paired rabbit cortical bone.

The optimal sterilization method for load bearing allografts remains a clinical concern. Recently, supercritical carbon dioxide (SCCO2) treatments have been shown to be capable of terminally sterilizing a range of bacteria and viruses, while preserving the static mechanical properties of cortical bone. This study evaluated the effect of SCCO2 treatment compared with two doses of gamma irradiation, on clinically relevant dynamic mechanical properties of cortical bone. Quasi-static testing was also performed to compare the impairment of treatment. Whole paired adult rabbit humeri were dissected and randomly assigned into either SCCO2 Control, SCCO2 Additive or gamma irradiation at 10 or 25kGy treatment groups. The bones were treated and mechanically tested in three-point bending, with the lefts acting as controls for the treated rights. Maximum load, energy to failure and stiffness were evaluated from static tests. The number of cycles to failure was determined for fatigue at 6-60% of the ultimate load. This study found that SCCO2 treatment with or without additive did not alter static or dynamic mechanical properties. Gamma irradiation had a deleterious dose dependent effect, with statistically significant (p<0.05) reductions in all static mechanical parameters at 25kGy. This effect was increased in fatigue with statistically significant decreases in both the 10 and 25kGy dose groups. This study highlights the expediency of SCCO2 treatment for load bearing bone allograft processing as terminal sterilization can be achieved while maintaining both the quasi-static and dynamic mechanical properties of the graft.

Effects of patellar position and defect healing on in vitro stifle joint kinematics following removal of the central one-third of the patellar tendon in an ovine model.

Harvest of the central one-third of the patella tendon (PT) is routinely performed for anterior cruciate ligament reconstruction (ACLR). Patella infera may ensue. In this study we unilaterally resected the central one-third of the PT in 20 sheep, without reconstructing or defunctionalizing the native ACL, and examined the effects at 3, 6, 12, and 24 weeks postoperatively on PT length, histological appearance of the donor defect and in vitro stifle joint kinematics. Mean length increases (p > 0.263) in the operated tendons of 0.3%, 2.8%, 0.5%, and 2.4% were observed at 3, 6, 12, and 24 weeks. A significant proximal shift of the patella correlated well with a mean 2.35° retardation of patellar flexion (r = 0.440, p = 0.001). A mean net 4.9° decrease in medial patellar tilt was also observed (p < 0.001), but was not coupled with changes in tibial rotation. Donor defect tissue showed a distinct progression of healing with time, remodeling from dense scar tissue at 3 weeks to bundles of well-organized collagen enveloped by vascularized loose connective tissue at 24 weeks but was not associated with the restoration of kinematics. These results suggest that resection of the central one-third of the PT and leaving the defect open in the ovine stifle joint may be associated with increased PT length and changes in patellar kinematics which do not recover 6 months postoperatively. The lack of patella infera may render this animal model unsuitable for the interpretation of joint kinematics following PT resection for human ACLR.

Effects of Gaps Induced Into the ACL Tendon Graft on Tendon-Bone Healing in a Rodent ACL Reconstruction Model.

Graft necrosis following ACL reconstruction is often associated with the use of autologous grafts. Host cells rather than graft cells contribute to the repair of the tendon-bone interface and the remodeling of the autologous graft. The native tendon-bone interface is not recreated and the biomechanical properties are not restored back to native values. We examined the effects of introducing gaps within the tendon graft prior to ACL reconstruction in a rodent model. We hypothesised that gaps will make physical way for host cells to infiltrate and repopulate the graft and thus enhance healing. Animals were sacrificed at seven, fourteen, and twenty-eight days for biomechanical testing and histology. Our findings indicate that graft necrosis, usually observed in the initial two weeks of the healing process, is averted. Histological observations showed that tendon-bone healing stages were hastened however this didn't translate into improved biomechanical properties.

Wound infusion with local anaesthesia after laparotomy: a randomized controlled trial.

BACKGROUND: The use of a continuous local anaesthesia infusion after laparotomy may reduce opioid requirements and facilitate earlier return of bowel function, independent mobilization and hospital discharge. METHODS: We performed a double-blinded, randomized controlled trial on 55 patients who underwent laparotomy. Patients were randomly allocated to receive a continuous infusion of either 0.2% ropivacaine or normal saline into their midline abdominal wound at the fascial level. The end points of the study were: total opioid requirements at 24 and 48 h; time to first flatus, bowel movement and independent ambulation; length of hospital stay; complications; and daily mean patient-reported pain scores at rest and movement. RESULTS: The two treatment groups were well controlled for factors that influence analgesia requirements, including age, weight, length of wound incision and type of operation. Patients allocated to ropivacaine infusion used, on average, 32 mg less morphine at 48 h (95% confidence interval 7, 57; P= 0.01). This was highly statistically significant after adjusting for age, gender and type of operation (P= 0.0006). Ropivacaine infusion was associated with a significantly decreased time to independent mobilization (P= 0.02), time to first flatus (P= 0.02) and reduced post-operative ileus (2/28 versus 9/27, χ(2) = 5.89, P= 0.02). There was no significant effect of ropivacaine infusion on time to first bowel movement (P= 0.94) nor length of hospital stay (P= 0.77). CONCLUSIONS: Local anaesthesia infusion at the fascial plane provides effective analgesia. This improves patient recovery through earlier return to bowel function and mobilization.

Mechanical properties of reconstructed achilles tendon with transfer of peroneus brevis or flexor hallucis longus tendon.

Treatment of chronic Achilles tendon ruptures can be technically difficult because of tendon retraction, atrophy, and short distal stumps. Surgical repair of chronic Achilles tendon ruptures focuses on local and free tendon transfers, as well as reconstruction with allografts or synthetic materials. This study examined the in vitro mechanical properties of a reconstructed Achilles tendon with the peroneus brevis or the flexor hallucis longus tendons in a human cadaver model. The tendons were harvested from 17 fresh-frozen human cadavers, and the same techniques were used for all of the model reconstructions. Biomechanical measurements included the failure load, stiffness, energy-to-peak load, and mode of failure. The mean failure load was significantly higher in the peroneus brevis group (P = .036), and there was no significant difference in stiffness and energy-to-peak load between the peroneus brevis and flexor hallucis longus groups. In every case, the mode of failure involved the tendon graft pulling through either the distal or proximal stump of the Achilles tendon. The greater failure loads observed with the use of peroneus brevis may not be clinically relevant, however, because of the magnitude of the peak loads observed in the cadaveric model. The present study supports the use of either peroneus brevis or flexor hallucis longus for reconstruction of chronic Achilles tendon ruptures and indicates the need for surgeons to carefully reinforce the attachment of the transferred tendon grafts to the stumps of the Achilles tendon to prevent pullout.