The effects of the method of fixation and interface conditions on the biomechanics of the femoral component of the Birmingham hip resurfacing arthroplasty were examined using a highly detailed three-dimensional computer model of the hip. Stresses and strains in the proximal femur were compared for the natural femur and for the femur resurfaced with the Birmingham hip resurfacing. A comparison of cemented versus uncemented fixation showed no advantage of either with regard to bone loading. When the Birmingham hip resurfacing femoral component was fixed to bone, proximal femoral stresses and strains were non-physiological. Bone resorption was predicted in the inferomedial and superolateral bone within the Birmingham hip resurfacing shell. Resorption was limited to the superolateral region when the stem was not fixed. The increased bone strain observed adjacent to the distal stem should stimulate an increase in bone density at that location. The remodelling of bone seen during revision of failed Birmingham hip resurfacing implants appears to be consistent with the predictions of our finite element analysis.

Many methods of reconstruction for ACL deficiency have been described, but little is known about their biomechanical properties. We examined extra-articular (EA), intra-articular (IA) and combined (EA+IA) reconstructions in ten cadaver knees after the ACL had been ruptured by the performance of a rapid anterior drawer movement. Stability at each stage before and after rupture and reconstruction was tested by anterior drawer, Lachman, varus-valgus and tibial rotation tests. Both IA and IA+EA reconstructions restored normal stability, while EA reconstructions improved stability but did not restore it to normal. The addition of an EA procedure to an IA procedure made no difference to knee stability. We conclude that in cases of isolated ACL deficiency there is no biomechanical basis for EA reconstruction, either alone or in addition to an IA reconstruction.

We have assessed the biomechanical properties of a 'double-bundle' prosthetic ligament replacing the anterior cruciate in cadaver knees. We compared the results with those of single bundle 'over-the-top' and 'through-the-condyle' techniques, performing anterior drawer tests at 20 degrees and 90 degrees knee flexion. The over-the-top reconstruction gave better anteroposterior stability at 20 degrees, while the through-the-condyle repair was more stable at 90 degrees. The double-bundle reconstruction gave practically normal anterior stability at both 20 degrees and 90 degrees.

We measured the initial fixation strength of a new graft, bone-hamstring-bone (BHB), for reconstruction of the anterior cruciate ligament (ACL) in 79 porcine knees and compared it with that of the normal porcine ACL and of the bone-patellar tendon-bone (BPB) graft. All specimens were subjected to ultimate load to failure and cyclic loading tests to assess the amount of graft slippage. The ultimate load to failure for the intact ACL was 1266 +/- 250 N, for the BPB graft 663 +/- 192 N and for the BHB graft 354 +/- 92 N (p < 0.01). After cycling to 235 N (the maximum load for all groups without failure) the average residual displacements after removal of the load for the ACL, BPB and BHB grafts were 0.031 +/- 0.013 cm, 0.078 +/- 0.033 cm, and 0.322 +/- 0.222 cm, respectively (p < 0.01). For the BHB graft the load to failure was less and the amount of graft slippage was more than for the BPB graft. Neither form of reconstruction was as strong as the intact ACL.

Aims

It has been well documented in the arthroplasty literature that lumbar degenerative disc disease (DDD) contributes to abnormal spinopelvic motion. However, the relationship between the severity or pattern of hip osteoarthritis (OA) as measured on an anteroposterior (AP) pelvic view and spinopelvic biomechanics has not been well investigated. Therefore, the aim of the study is to examine the association between the severity and pattern of hip OA and spinopelvic motion.

We studied the effects of high-dose irradiation on the mechanical properties and morphology of cortical bone in rabbits for 52 weeks after a single dose of 50 Gy of electron-beam to the tibia. After four weeks, the bending strength of the irradiated bone was unchanged, but at 12 weeks, the strength had decreased significantly. At 24 weeks after irradiation mean strength was less than half of controls but by 52 weeks there was a tendency toward recovery. Similar, synchronous changes of damage and recovery were seen in cortical porosity, haematopoietic cells in the bone marrow and endosteal new bone formation.

Aims

In patients with a rotator cuff tear, tear pattern and tendon involvement are known risk factors for the development of pseudoparalysis of the shoulder. It remains unclear, however, why similar tears often have very different functional consequences. The present study hypothesizes that individual shoulder anatomy, specifically the moment arms (MAs) of the rotator cuff (RC) and the deltoid muscle, as well as their relative recruitment during shoulder abduction, plays a central role in pseudoparalysis.

Aims

A retrospective longitudinal study was conducted to compare directly volumetric wear of retrieved polyethylene inserts to predicted volumetric wear modelled from individual gait mechanics of total knee arthroplasty (TKA) patients.

Aims

The aim of this study was to assess the effect of posterior cruciate ligament (PCL) resection on flexion-extension gaps, mediolateral soft-tissue laxity, fixed flexion deformity (FFD), and limb alignment during posterior-stabilized (PS) total knee arthroplasty (TKA).

Aims

The surgical management of ankle arthritis with tibiotalar arthrodesis is known to alter gait, as compared with normal ankles. The purpose of this study was to assess post-operative gait function with gait before arthrodesis.

In this study we used subject-specific finite element analysis to investigate the mechanical effects of rotational acetabular osteotomy (RAO) on the hip joint and analysed the correlation between various radiological measurements and mechanical stress in the hip joint.

We evaluated 13 hips in 12 patients (two men and ten women, mean age at surgery 32.0 years; 19 to 46) with developmental dysplasia of the hip (DDH) who were treated by RAO.

Subject-specific finite element models were constructed from CT data. The centre–edge (CE) angle, acetabular head index (AHI), acetabular angle and acetabular roof angle (ARA) were measured on anteroposterior pelvic radiographs taken before and after RAO. The relationship between equivalent stress in the hip joint and radiological measurements was analysed.

The equivalent stress in the acetabulum decreased from 4.1 MPa (2.7 to 6.5) pre-operatively to 2.8 MPa (1.8 to 3.6) post-operatively (p < 0.01). There was a moderate correlation between equivalent stress in the acetabulum and the radiological measurements: CE angle (R = –0.645, p < 0.01); AHI (R = –0.603, p < 0.01); acetabular angle (R = 0.484, p = 0.02); and ARA (R = 0.572, p < 0.01).

The equivalent stress in the acetabulum of patients with DDH decreased after RAO. Correction of the CE angle, AHI and ARA was considered to be important in reducing the mechanical stress in the hip joint.

Cite this article: Bone Joint J 2015;97-B:492–7.

Cementless femoral stems are currently preferred for total hip replacement (THR) in the United States. Improvements in stem design, instrumentation and surgical technique have made this technology highly successful, reproducible, and applicable to the vast majority of patients requiring a THR. However, there are ongoing developments in some aspects of stem design that influence clinical results, the incidence of complications and their inherent adaptability in accommodating the needs of individual patients. Here we examine some of these design features.

Cite this article: Bone Joint J 2013;95-B, Supple A:53–6.

The augmentation of fixation with bone cement is increasingly being used in the treatment of severe osteoporotic fractures. We investigated the influence of bone quality on the mechanics of augmentation of plate fixation in a distal femoral fracture model (AO 33 A3 type). Eight osteoporotic and eight non-osteoporotic femoral models were randomly assigned to either an augmented or a non-augmented group. Fixation was performed using a locking compression plate. In the augmented group additionally 1 ml of bone cement was injected into the screw hole before insertion of the screw. Biomechanical testing was performed in axial sinusoidal loading. Augmentation significantly reduced the cut-out distance in the osteoporotic models by about 67% (non-augmented mean 0.30 mm (sd 0.08) vs augmented 0.13 mm (sd 0.06); p = 0.017). There was no statistical reduction in this distance following augmentation in the non-osteoporotic models (non-augmented mean 0.15 mm (sd 0.02) vs augmented 0.15 mm (sd 0.07); p = 0.915). In the osteoporotic models, augmentation significantly increased stability (p = 0.017).

Cite this article: Bone Joint J 2013;95-B:1406–9.

It has been suggested that extracorporeal shockwave therapy is a safe and effective treatment for pain relief from recalcitrant plantar fasciopathy (PF). However, the changes in gait and associated biomechanical parameters have not been well characterised. We recruited 12 female patients with recalcitrant PF who had a mean age of 59 years (50 to 70) and mean body mass index of 25 kg/m² (22 to 30). The patients reported a mean duration of symptoms of 9.3 months (6 to 15). Shockwave therapy consisting of 1500 impulses (energy flux density 0.26 mJ/mm²) was applied for three sessions, each three weeks apart. A pain visual analogue scale (VAS) rating, plantar pressure assessment and motion analysis were carried out before and nine weeks after first shock wave therapy. It was demonstrated that patients increased their walking velocity and cadence as well indicating a decrease in pain after shockwave therapy. In the symptomatic foot, the peak contact pressure over the forefoot increased and the contact area over the digits decreased. The total foot impulse also decreased as did stance duration. The duration the centre of pressure remained in the hindfoot increased in the symptomatic foot after shockwave therapy. The differences in centre of pressure trajectory at baseline decreased at final follow-up. In conclusion, shockwave therapy not only decreased the pain VAS rating but also improved the gait parameters of the symptomatic foot in PF patients.

Cite this article: Bone Joint J 2013;95-B:1088–93.

The lateral compartment is predominantly affected in approximately 10% of patients with osteoarthritis of the knee. The anatomy, kinematics and loading during movement differ considerably between medial and lateral compartments of the knee. This in the main explains the relative protection of the lateral compartment compared with the medial compartment in the development of osteoarthritis. The aetiology of lateral compartment osteoarthritis can be idiopathic, usually affecting the femur, or secondary to trauma commonly affecting the tibia. Surgical management of lateral compartment osteoarthritis can include osteotomy, unicompartmental knee replacement and total knee replacement. This review discusses the biomechanics, pathogenesis and development of lateral compartment osteoarthritis and its management.

Cite this article: Bone Joint J 2013;95-B:436–44.

Progressive retroversion of a cemented stem is predictive of early loosening and failure. We assessed the relationship between direct post-operative stem anteversion, measured with CT, and the resulting rotational stability, measured with repeated radiostereometric analysis over ten years. The study comprised 60 cemented total hip replacements using one of two types of matt collared stem with a rounded cross-section. The patients were divided into three groups depending on their measured post-operative anteversion (< 10°, 10° to 25°, >  25°). There was a strong correlation between direct post-operative anteversion and later posterior rotation. At one year the < 10° group showed significantly more progressive retroversion together with distal migration, and this persisted to the ten-year follow-up. In the < 10° group four of ten stems (40%) had been revised at ten years, and an additional two stems (20%) were radiologically loose. In the ‘normal’ (10° to 25°) anteversion group there was one revised (3%) and one loose stem (3%) of a total of 30 stems, and in the > 25° group one stem (5%) was revised and another loose (5%) out of 20 stems. This poor outcome is partly dependent on the design of this prosthesis, but the results strongly suggest that the initial rotational position of cemented stems during surgery affects the subsequent progressive retroversion, subsidence and eventual loosening. The degree of retroversion may be sensitive to prosthetic design and stem size, but < 10° of anteversion appears deleterious to the long-term outcome for cemented hip prosthetic stems.

Cite this article: Bone Joint J 2013;95-B:23–30.

Reverse total shoulder replacement (RTSR) depends on adequate deltoid function for a successful outcome. However, the anterior deltoid and/or axillary nerve may be damaged due to prior procedures or injury. The purpose of this study was to determine the compensatory muscle forces required for scapular plane elevation following RTSR when the anterior deltoid is deficient. The soft tissues were removed from six cadaver shoulders, except for tendon attachments. After implantation of the RTSR, the shoulders were mounted on a custom-made shoulder simulator to determine the mean force in each muscle required to achieve 30° and 60° of scapular plane elevation. Two conditions were tested: 1) Control with an absent supraspinatus and infraspinatus; and 2) Control with anterior deltoid deficiency. Anterior deltoid deficiency resulted in a mean increase of 195% in subscapularis force at 30° when compared with the control (p = 0.02). At 60°, the subscapularis force increased a mean of 82% (p < 0.001) and the middle deltoid force increased a mean of 26% (p = 0.04).

Scapular plane elevation may still be possible following an RTSR in the setting of anterior deltoid deficiency. When the anterior deltoid is deficient, there is a compensatory increase in the force required by the subscapularis and middle deltoid. Attempts to preserve the subscapularis, if present, might maximise post-operative function.

Aims

Surgical approaches that claim to be minimally invasive, such as the direct anterior approach (DAA), are reported to have a clinical advantage, but are technically challenging and may create more injury to the soft-tissues during joint exposure. Our aim was to quantify the effect of soft-tissue releases on the joint torque and femoral mobility during joint exposure for hip resurfacing performed via the DAA.

Aims

The aim of this study was to investigate the impact of the level of upper instrumented vertebra (UIV) in frail patients undergoing surgery for adult spine deformity (ASD).

Aims

This study aimed to quantify the shoulder kinematics during an apprehension-relocation test in patients with anterior shoulder instability (ASI) and glenoid bone loss using the radiostereometric analysis (RSA) method. Kinematics were compared with the patient’s contralateral healthy shoulder.

Aims

Postoperative complication rates remain relatively high after adult spinal deformity (ASD) surgery. The extent to which modifiable patient-related factors influence complication rates in patients with ASD has not been effectively evaluated. The aim of this retrospective cohort study was to evaluate the association between modifiable patient-related factors and complications after corrective surgery for ASD.

Aims

Custom flange acetabular components (CFACs) are a patient-specific option for addressing large acetabular defects at revision total hip arthroplasty (THA), but patient and implant characteristics that affect survivorship remain unknown. This study aimed to identify patient and design factors related to survivorship.

Aims

The hip’s capsular ligaments passively restrain extreme range of movement (ROM) by wrapping around the native femoral head/neck. We determined the effect of hip resurfacing arthroplasty (HRA), dual-mobility total hip arthroplasty (DM-THA), conventional THA, and surgical approach on ligament function.

Aims

We report the clinical results of glenoid osteotomy in patients with atraumatic posteroinferior instability associated with glenoid dysplasia.

Aims

Our aim was to evaluate the radiographic characteristics of patients undergoing total hip arthroplasty (THA) for the potential of posterior bony impingement using CT simulations.

We evaluated the accuracy with which a custom-made acetabular component could be positioned at revision arthroplasty of the hip in patients with a Paprosky type 3 acetabular defect.

A total of 16 patients with a Paprosky type 3 defect underwent revision surgery using a custom-made trabecular titanium implant. There were four men and 12 women with a median age of 67 years (48 to 79). The planned inclination (INCL), anteversion (AV), rotation and centre of rotation (COR) of the implant were compared with the post-operative position using CT scans.

A total of seven implants were malpositioned in one or more parameters: one with respect to INCL, three with respect to AV, four with respect to rotation and five with respect to the COR.

To the best of our knowledge, this is the first study in which CT data acquired for the pre-operative planning of a custom-made revision acetabular implant have been compared with CT data on the post-operative position. The results are encouraging.

Cite this article: Bone Joint J 2015; 97-B:780–5.

There are three basic concepts that are important to the biomechanics of pedicle screw-based instrumentation. First, the outer diameter of the screw determines pullout strength, while the inner diameter determines fatigue strength. Secondly, when inserting a pedicle screw, the dorsal cortex of the spine should not be violated and the screws on each side should converge and be of good length. Thirdly, fixation can be augmented in cases of severe osteoporosis or revision.

A trajectory parallel or caudal to the superior endplate can minimise breakage of the screw from repeated axial loading. Straight insertion of the pedicle screw in the mid-sagittal plane provides the strongest stability.

Rotational stability can be improved by adding transverse connectors. The indications for their use include anterior column instability, and the correction of rotational deformity.

We evaluated the top 13 journals in trauma and orthopaedics by impact factor and looked at the longer-term effect regarding citations of their papers.

All 4951 papers published in these journals during 2007 and 2008 were reviewed and categorised by their type, subspecialty and super-specialty. All citations indexed through Google Scholar were reviewed to establish the rate of citation per paper at two, four and five years post-publication. The top five journals published a total of 1986 papers. Only three (0.15%) were on operative orthopaedic surgery and none were on trauma. Most (n = 1084, 54.5%) were about experimental basic science. Surgical papers had a lower rate of citation (2.18) at two years than basic science or clinical medical papers (4.68). However, by four years the rates were similar (26.57 for surgery, 30.35 for basic science/medical), which suggests that there is a considerable time lag before clinical surgical research has an impact.

We conclude that high impact journals do not address clinical research in surgery and when they do, there is a delay before such papers are cited. We suggest that a rate of citation at five years post-publication might be a more appropriate indicator of importance for papers in our specialty.

Cite this article: Bone Joint J 2014;96-B:414–19.

Many different lengths of stem are available for use in primary total hip replacement, and the morphology of the proximal femur varies greatly. The more recently developed shortened stems provide a distribution of stress which closely mimics that of the native femur. Shortening the femoral component potentially comes at the cost of decreased initial stability. Clinical studies on the performance of shortened cemented and cementless stems are promising, although long-term follow-up studies are lacking. We provide an overview of the current literature on the anatomical features of the proximal femur and the biomechanical aspects and clinical outcomes associated with the length of the femoral component in primary hip replacement, and suggest a classification system for the length of femoral stems.

Cite this article: Bone Joint J 2014;96-B:442-8.

Large femoral heads have been used with increasing frequency over the last decade. The prime reason is likely the effect of large heads on stability. The larger head neck ratio, combined with the increased jump distance of larger heads result in a greater arc of impingement free motion, and greater resistance to dislocation in a provocative position. Multiple studies have demonstrated clear clinical efficacy in diminishing dislocation rates with the use of large femoral heads. With crosslinked polyethylene, wear has been shown to be equivalent between larger and smaller heads. However, the stability advantages of increasing diameter beyond 38 mm have not been clearly demonstrated. More importantly, recent data implicates large heads in the increasing prevalence of groin pain and psoas impingement. There are clear benefits with larger femoral head diameters, but the advantages of diameters beyond 38 mm have not yet been demonstrated clinically.

The sternoclavicular joint (SCJ) is a pivotal articulation in the linked system of the upper limb girdle, providing load-bearing in compression while resisting displacement in tension or distraction at the manubrium sterni. The SCJ and acromioclavicular joint (ACJ) both have a small surface area of contact protected by an intra-articular fibrocartilaginous disc and are supported by strong extrinsic and intrinsic capsular ligaments. The function of load-sharing in the upper limb by bulky periscapular and thoracobrachial muscles is extremely important to the longevity of both joints. Ligamentous and capsular laxity changes with age, exposing both joints to greater strain, which may explain the rising incidence of arthritis in both with age. The incidence of arthritis in the SCJ is less than that in the ACJ, suggesting that the extrinsic ligaments of the SCJ provide greater stability than the coracoclavicular ligaments of the ACJ.

Instability of the SCJ is rare and can be difficult to distinguish from medial clavicular physeal or metaphyseal fracture-separation: cross-sectional imaging is often required. The distinction is important because the treatment options and outcomes of treatment are dissimilar, whereas the treatment and outcomes of ACJ separation and fracture of the lateral clavicle can be similar. Proper recognition and treatment of traumatic instability is vital as these injuries may be life-threatening. Instability of the SCJ does not always require surgical intervention. An accurate diagnosis is required before surgery can be considered, and we recommend the use of the Stanmore instability triangle. Most poor outcomes result from a failure to recognise the underlying pathology.

There is a natural reluctance for orthopaedic surgeons to operate in this area owing to unfamiliarity with, and the close proximity of, the related vascular structures, but the interposed sternohyoid and sternothyroid muscles are rarely injured and provide a clear boundary to the medial retroclavicular space, as well as an anatomical barrier to unsafe intervention.

This review presents current concepts of instability of the SCJ, describes the relevant surgical anatomy, provides a framework for diagnosis and management, including physiotherapy, and discusses the technical challenges of operative intervention.

Cite this article: Bone Joint J 2013;95-B:721–31.

This paper outlines the recent development of an exchange Travelling Fellowship scheme between the British and American Orthopaedic Research Societies.

We used demineralised bone matrix (DBM) to augment re-attachment of tendon to a metal prosthesis in an in vivo ovine model of reconstruction of the extensor mechanism at the knee. We hypothesised that augmentation of the tendon-implant interface with DBM would enhance the functional and histological outcomes as compared with previously reported control reconstructions without DBM. Function was assessed at six and 12 weeks postoperatively, and histological examination was undertaken at 12 weeks.

A significant increase of 23.5% was observed in functional weight-bearing at six weeks in the DBM-augmented group compared with non-augmented controls (p = 0.004). By 12 weeks augmentation with DBM resulted in regeneration of a more direct-type enthesis, with regions of fibrocartilage, mineralised fibrocartilage and bone. In the controls the interface was predominantly indirect, with the tendon attached to the bone graft-hydroxyapatite base plate by perforating collagen fibres.

The management of injury to the distal tibiofibular syndesmosis remains controversial in the treatment of ankle fractures. Operative fixation usually involves the insertion of a metallic diastasis screw. There are a variety of options for the position and characterisation of the screw, the type of cortical fixation, and whether the screw should be removed prior to weight-bearing. This paper reviews the relevant anatomy, the clinical and radiological diagnosis and the mechanism of trauma and alternative methods of treatment for injuries to the syndesmosis.

Advances in hip arthroscopy have renewed interest in the ligamentum teres. Considered by many to be a developmental vestige, it is now recognised as a significant potential source of pain and mechanical symptoms arising from the hip joint. Despite improvements in imaging, arthroscopy remains the optimum method of diagnosing lesions of the ligamentum teres. Several biological or mechanical roles have been proposed for the ligament. Unless these are disproved, the use of surgical procedures that sacrifice the ligamentum teres, as in surgical dislocation of the hip, should be carefully considered. This paper provides an update on the development, structure and function of the ligamentum teres, and discusses associated clinical implications.

Mobile-bearing posterior-stabilised knee replacements have been developed as an alternative to the standard fixed- and mobile-bearing designs. However, little is known about the in vivo kinematics of this new group of implants. We investigated 31 patients who had undergone a total knee replacement with a similar prosthetic design but with three different options: fixed-bearing posterior cruciate ligament-retaining, fixed-bearing posterior-stabilised and mobile-bearing posterior-stabilised. To do this we used a three-dimensional to two-dimensional model registration technique. Both the fixed- and mobile-bearing posterior-stabilised configurations used the same femoral component. We found that fixed-bearing posterior stabilised and mobile-bearing posterior-stabilised knee replacements demonstrated similar kinematic patterns, with consistent femoral roll-back during flexion. Mobile-bearing posterior-stabilised knee replacements demonstrated greater and more natural internal rotation of the tibia during flexion than fixed-bearing posterior-stabilised designs. Such rotation occurred at the interface between the insert and tibial tray for mobile-bearing posterior-stabilised designs. However, for fixed-bearing posterior-stabilised designs, rotation occurred at the proximal surface of the bearing. Posterior cruciate ligament-retaining knee replacements demonstrated paradoxical sliding forward of the femur.

We conclude that mobile-bearing posterior-stabilised knee replacements reproduce internal rotation of the tibia more closely during flexion than fixed-bearing posterior-stabilised designs. Furthermore, mobile-bearing posterior-stabilised knee replacements demonstrate a unidirectional movement which occurs at the upper and lower sides of the mobile insert. The femur moves in an anteroposterior direction on the upper surface of the insert, whereas the movement at the lower surface is pure rotation. Such unidirectional movement may lead to less wear when compared with the multidirectional movement seen in fixed-bearing posterior-stabilised knee replacements, and should be associated with more evenly applied cam-post stresses.

We used an in vivo model to assess the use of an autogenous cancellous bone block and marrow graft for augmenting tendon reattachment to metallic implants. We hypothesised that augmentation of the tendon-implant interface with a bone block would enable retention of the graft on the implant surface, enhance biological integration, and result in more consistent functional outcomes compared with previously reported morcellised graft augmentation techniques.

A significant improvement in functional weight-bearing was observed between six and 12 weeks. The significant increase in ground reaction force through the operated limb between six and 12 weeks was greater than that reported previously with morcellised graft augmented reconstructions. Histological appearance and collagen fibre orientation with bone block augmentation more closely resembled that of an intact enthesis compared with the morcellised grafting technique. Bone block augmentation of tendon-implant interfaces results in more reliable functional and histological outcomes, with a return to pre-operative levels of weight-bearing by 24 weeks.

Posterolateral rotatory instability is the most common type of symptomatic chronic instability of the elbow. In this condition the forearm complex rotates externally in relation to the humerus, causing posterior subluxation or dislocation of the radial head. The lateral ligament complex, radial head and coronoid process are important constraints to posterolateral rotatory instability, and their disruption is involved in the pathogenesis of this condition. The diagnosis relies on a high index of clinical suspicion, active and passive apprehension tests, and examination under anaesthesia. Surgical treatment has given consistently successful results. Open reconstruction of the lateral ligaments with a tendon graft has been the procedure of choice, with arthroscopic techniques emerging as a potential alternative.

The ability to predict load-bearing capacity during the consolidation phase in distraction osteogenesis by non-invasive means would represent a significant advance in the management of patients undergoing such treatment. Measurements of stiffness have been suggested as a promising tool for this purpose. Although the multidimensional characteristics of bone loading in compression, bending and torsion are apparent, most previous experiments have analysed only the relationship between maximum load-bearing capacity and a single type of stiffness. We have studied how compressive, bending and torsional stiffness are related to the torsional load-bearing capacity of healing callus using a common set of samples of bone regenerate from 26 sheep treated by tibial distraction osteogenesis.

Our findings showed that measurements of torsional, bending and compressive stiffness were all suitable as predictors of the load-bearing capacity of healing callus. Measurements of torsional stiffness performed slightly better than those of compressive and bending stiffness.

We examined the mechanical properties of Vicryl (polyglactin 910) mesh in vitro and assessed its use in vivo as a novel biomaterial to attach tendon to a hydroxyapatite-coated metal implant, the interface of which was augmented with autogenous bone and marrow graft. This was compared with tendon re-attachment using a compressive clamp device in an identical animal model. Two- and four-ply sleeves of Vicryl mesh tested to failure under tension reached 5.13% and 28.35% of the normal ovine patellar tendon, respectively. Four-ply sleeves supported gait in an ovine model with 67.05% weight-bearing through the operated limb at 12 weeks, without evidence of mechanical failure.

Mesh fibres were visible at six weeks but had been completely resorbed by 12 weeks, with no evidence of chronic inflammation. The tendon-implant neoenthesis was predominantly an indirect type, with tendon attached to the bone-hydroxyapatite surface by perforating collagen fibres.

We developed an in vivo model of the attachment of a patellar tendon to a metal implant to simulate the reconstruction of an extensor mechanism after replacement of the proximal tibia. In 24 ewes, the patellar tendon was attached to a hydroxyapatite (HA)-coated titanium prosthesis. In 12, the interface was augmented with autograft containing cancellous bone and marrow. In the remaining ewes, the interface was not grafted.

Kinematic gait analysis showed nearly normal function of the joint by 12 weeks. Force-plate assessment showed a significant increase in functional weight-bearing in the grafted animals (p = 0.043). The tendon-implant interface showed that without graft, encapsulation of fibrous tissue occurred. With autograft, a developing tendon-bone-HA-implant interface was observed at six weeks and by 12 weeks a layered tendon-fibrocartilage-bone interface was seen which was similar to a direct-type enthesis.

With stable mechanical fixation, an appropriate bioactive surface and biological augmentation the development of a functional tendon-implant interface can be achieved.