Introduction. There is widespread variation in the management of rare orthopaedic disease, in a large part owing to uncertainty. No individual surgeon or hospital is typically equipped to amass sufficient numbers of cases to draw robust conclusions from the information available to them. The programme of research will establish the British Orthopaedic Surgery Surveillance (BOSS) Study; a nationwide reporting structure for rare disease in orthopaedic surgery. Methods. The BOSS Study is a series of nationwide observational cohort studies of pre-specified orthopaedic disease. All relevant hospitals treating the disease are invited to contribute anonymised case details. Data will be collected digitally through REDCap, with an additional bespoke software solution used to regularly confirm case ascertainment, prompt follow-up reminders and identify potential missing cases from external sources of information (i.e. national administrative data). With their consent, patients will be invited to enrich the data collected by supplementing anonymised case data with patient reported outcomes. The study will primarily seek to calculate the incidence of the rare diseases under investigation, with 95% confidence intervals. Descriptive statistics will be used to describe the case mix, treatment variations and outcomes. Inferential statistical analysis may be used to analyze associations between presentation factors and outcomes. Types of analyses will be contingent on the disease under investigation. Discussion. This study builds upon other national rare disease supporting structures, particularly those in obstetrics and paediatric surgery. It is particularly focused on addressing the evidence base for quality and safety of surgery, and the design is influenced by the specifications of the IDEAL collaboration for the development of surgical research

Aims

The aim of this study was to evaluate the epidemiology and treatment of Perthes’ disease of the hip.

Aims

The aim of this study was to inform the epidemiology and treatment of slipped capital femoral epiphysis (SCFE).

Aims. Slipped capital femoral epiphysis (SCFE) is one of the most common hip diseases of adolescence that can cause marked disability, yet there is little robust evidence to guide treatment. Fundamental aspects of the disease, such as frequency, are unknown and consequently the desire of clinicians to undertake robust intervention studies is somewhat prohibited by a lack of fundamental knowledge. Methods. The study is an anonymized nationwide comprehensive cohort study with nested consented within the mechanism of the British Orthopaedic Surgery Surveillance (BOSS) Study. All relevant hospitals treating SCFE in England, Scotland, and Wales will contribute anonymized case details. Potential missing cases will be cross-checked against two independent external sources of data (the national administrative data and independent trainee data). Patients will be invited to enrich the data collected by supplementing anonymized case data with patient-reported outcome measures. In line with recommendations of the IDEAL Collaboration, the study will primarily seek to determine incidence, describe case mix and variations in surgical interventions, and explore the relationships between baseline factors (patients and types of interventions) and two-year outcomes. Discussion. This is the first disease to be investigated using the BOSS Study infrastructure. It provides a robust method to determine the disease frequency, and a large unbiased sample of cases from which treatment strategies can be investigated. It may form the basis for definitive robust intervention studies or, where these are demonstrated not to be feasible, this may be the most robust cohort study

The Medial Patellofemoral Ligament (MPFL) is the main restraining force against lateral patellar displacement. It is often disrupted following patellar subluxation or dislocation. MPFL reconstruction is frequently performed when conservative management fails and the patient experiences recurrent patellar dislocation. Various MPFL reconstruction procedures have been described in the literature and reported outcomes are encouraging. This study analyses the radiographic outcomes following MPFL reconstruction. From January 2006 to January 2011, 76 consecutive patients (80 knees) with patellar recurrent dislocation underwent medial patellofemoral ligament reconstruction in three large teaching hospitals. Mean follow-up was 31.8 months (range, 13–72). Semitendinosus and gracilis autografts were used for the reconstruction and all procedures were carried out by the senior authors (WL, BR, CW, MB). Plain radiographs (Anteroposterior (AP), Lateral and Skyline) performed preoperatively and postoperatively were used to compare the sulcus angle, congruence angle, lateral patellofemoral angle, trochlear dysplasia (Dejour classification), trochlear boss height and patellar height (Caton-Deschamps ratio). Plain radiographs (Lateral) performed postoperatively were used to evaluate the femoral tunnel placement used for MPFL reconstruction. The sulcus angle improved from 143.2° (122.9–157.7) to 139.3° (115.7–154.6) and the congruence angle improved from 26.7° (−17.5–82.6) to 0.26° (−35.3–7.8). The lateral patellofemoral angle was 7.99° (3.2–19.2) preoperatively and 9.02° (3.2–18.2) postoperatively. The Caton-Deschamps ratio was 1.2 (1.0–1.5) preoperatively and 1.0 (0.8–1.1) postoperatively. Using the Dejour classification of trochlear dysplasia, all preoperative radiographs were considered to be grade C or D and all postoperative radiographs were considered to be grade A or B. Trochlear boss height was 5.9mm (1.8–11.6) preoperatively and 4.7mm (1.6–6.9) postoperatively. 59% of the femoral tunnels were considered to be in a good position on postoperative radiographs. This study displayed a significant improvement in postoperative radiographic parameters, demonstrating the importance of anatomic restoration when performing MPFL reconstruction

Background. Patellar instability is a complex, multi-factorial disorder. Radiological assessment is regarded as an important part of the management of this population. The purpose of this study was to determine the intra- and inter-rater reliability of common radiological measurements used to evaluate patellar instability. Methods. One hundred and fifty x-rays from 51 individuals were reviewed by five reviewers: two orthopaedic trainees, a radiological trainee, a consultant radiologist and an orthopaedic physiotherapist. Radiological measurements assessed included patellar shape, sulcus angle, congruence angle, lateral patellofemoral angle (LPA), lateral patellar displacement (LPD), lateral displacement measurement (LDM), boss height, and patellar height ratios (Caton-Deschamps, Blackburne-Peel, Insall-Salvati). All assessors were provided with a summary document outlining the method of assessing each measurement. Bland-Altman analyses were adopted to assess intra- and inter-rater reliability. Results. The results indicated generally low measurement error on intra-rater reliability assessment, particularly for LPD (within-subject variance 0.7mm to 3.7mm), LDM (0.7mm to 3.5mm) and boss height (0.4mm to 1.6mm) for all assessors. There was greater measurement error for the calculation of sulcus angle (0.7° to 10.6°), congruence angle (0.8° to 18.4°) and LPA (0.8° to 16.5°). Whilst the inter-rater reliability between assessors indicated a low mean difference for assessments of patellar height measurements (0.0° to 0.6°), there was greater variability for LPA (0.1° to 3.6°), LPD (0.2mm to 4.6mm) and LDM (0.1mm to 4.0mm), with wide 95% limits of agreement for all measurements indicated poor precision. Conclusions. Many of the standard measurements used to assess the patellofemoral joint on plain radiographs have poor precision. Intra-rater reliability may be related to experience but it seems likely that to achieve good inter-rater reliability, specific training may be required to calibrate observers. More formal training in the technique of radiological measurement for those who were inexperienced might have improved the inter-rater reliability

Imaging techniques including MR scanning and ultrasound were discussed. However it was noted that for standard orthopaedic practice in the UK plain films were the initial imaging available. The importance of taking a skyline view was stressed. The Dejour protocol was then outlined where the lateral Xray of the knee assesses the patellar height, the presence of dysplasia of the trochlear groove, and, if present, its boss height. A CT scan defines the patellar tilt angle, and with cuts through the tibial tubercle, the offset of the tibial tubercle from the trochlear groove (TTTG). The four abnormalities that can be defined are then corrected at operation. All patients undergo a lateral release. If the patellar tilt angle is greater than 20° then a medial reefing is performed. If the patellar height is greater than 1.2, a distalisation of the tibial tubercle to correct this to 1.0 is done. A MG of greater than 2Omm leads to a correction by an Elmsie medial tubercle transfer. A boss height of greater than 6mm suggests a trochleoplasty should be performed. However the Dejour protocol is yet to be validated. It was concluded that imaging is essential for analysing patellofemoral instability. Plain films alone do not give enough information. Patterns of patellofemoral instability as assessed by CT scan (and MRI scan) are yet to be established. Postoperative imaging to confirm correction of abnormalities should be done. The measurements are worthwhile but their validation is awaited

Introduction and Aims: Dysplasia of the femoral sulcus is one component that may be present in patients presenting with patellar instability. Rarely the dysplasia is so severe that a dome rather than groove is present. Dejour has reported an operation that deepens the groove, unlike the Albee which elevates it. This study reports the development of a modification of the Dejour trochleoplasty reporting the clinical and radiological results. Method: A consecutive case series of the first 15 patients (17 knees) who underwent a trochleoplasty with a minimum one-year follow-up. There were 11 females and four males with an age range from 15 to 47 years old. Nine patients had had previous operations. The pre-operative length of symptoms ranged from one to 30 years. The patellar instability was managed operatively using the Dejour protocol measuring the patellar height, boss height, tibial tubercle-trochlear groove distance and patellar tilt angle. The Kujala score was used for functional assessment and a subjective assessment was also made. CT scans as well as plain films were used for radiological assessment. The operative technique changed in the light of experience from metallic to absorbable screws as the former abraded the patella. Results: The boss height was reduced from an average of 7.5mm to 1mm (normal 0mm). Tracking became normal in 11 knees and had a slight J-shape in six. Seven knees had a mild residual apprehension. Five patients were very satisfied, eight were satisfied, and two were disappointed. The Kujala score improved from an average of 48 to 73 out of 100. Three patients returned to full sports. Eight patients required further operations apart from the removal of metallic screws in 10 knees. Five of these were arthrolysis for stiffness at about six weeks post-operatively. As a result, patients were placed on a continuous passive motion machine for three to four days to avoid this. One patient went on to have autologous chondrocyte implantation for a defect on the lateral femoral condyle involving the tibial surface. This was after a new injury following a return to sports and not in the area affected by the trochleoplasty. Conclusion: Trochleoplasty for severe dysplasia of the femoral sulcus is a developing procedure. It requires careful attention to detail. For a rare condition the results have been gratifying with an acceptable level of complications. It is not recommended that this procedure be performed by general orthopaedic surgeons

Purpose. To assess the use of radiographic measurement compared to descriptive classification in the evaluation of Perthes' disease. Method. Fifteen consultant Paediatric Orthopaedic surgeons, members of the BOSS Collaborative from different UK centres, were asked to rate a series of 100 healed AP radiographs of hips affected by Perthes' Disease from the Liverpool Perthes' Disease Register using the Stulberg' s grading. Two independent observers categorised roundness error using Digitimizer™ software. Kappa scores were used to determine the inter-observer concordance amongst the 15 observers for Stulberg classification. Lin concordance was used to determine roundness error assessment. The relationship between the two outcomes was explored statistically and graphically; considering the mean Stulberg grade recorded by the 15 observers as a continuous outcome. Results. There was moderate to fair agreement regarding the Stulberg' s grading among the Consultant surgeons with an overall Kappa error of 0.377 (95% 0.353 – 0.393). The Lin concordance between the two independent observers evaluating roundness error was 0.50 (95% CI 0.36–0.64). There was a strong correlation between the Stulberg grading and roundness error measurement. Using a box and whisker chart the roundness error correlated well with modal Stulberg grade. Conclusion. Roundness error appears to be a useful radiographic measure of hip shape in Perthes' disease by offering a continuous estimate of hip deformity. It correlates well with surgeon-reported hip shape and can be a useful tool in clinical trials

The battle of revision TKA is won or lost with safe, effective, and minimally bony-destructive implant removal, protecting all ligamentous stabilisers of the knee and, most importantly, the extensor mechanism. For exposure, incisions should be long and generous to allow adequate access. A standard medial parapatellar capsular arthrotomy is preferred. A synovectomy is performed followed by debridement of all scar tissue, especially in the medial and lateral gutters. All peripatellar scar tissue is excised followed by release of scar tissue within the patellar tendon, allowing for displacement or everting of the patella. As patellar tendon avulsion at any time of knee surgery yields disastrous results, the surgeon should be continuously evaluating the patellar tendon integrity, especially while displacing/everting the patella and bringing the knee into flexion. If displacement/eversion is difficult, consider rectis-snip, V-Y quadricepsplasty, or tibial tubercle osteotomy. The long-held requisite for patellar eversion prior to component removal is inaccurate. In most cases simple lateral patellar subluxation will provide adequate exposure. If a modular tibial system is involved, removal of the tibial polyethylene will decompress the knee, allowing for easier access to patellar, femoral, and tibial components. For patellar component removal, first identify the border of the patella, then carefully clean and debride the interface, preferably with electrocautery. If the tibial component is cemented all-polyethylene, remove using an oscillating saw at the prosthetic-bone interface. Debride the remaining cement with hand tools, ultrasonic tools, or burrs. Remove the remaining peg using a low-speed burr. If the tibial component is metal-backed, then utilise a thin saw blade or reciprocating saw to negotiate the undersurface of the component between the pegs. If pegs are peripherally located, cut with a diamond disc circular cutting tool. Use a trephine to remove the pegs. For femoral component removal, identify the prosthetic-bone/prosthetic-cement interface then remove soft tissue from the interface, preferably with electrocautery. Disrupt the interface around all aspects of the component, using any of following: Gigli saw for cementless components only, micro saw, standard oscillating saw, reciprocating saw, a series of thin osteotomes, or ultrasonic equipment. If the femoral component is stemmed, remove the component in two segments using an appropriate screwdriver to remove the screw locking the stem to the component. Remove the femoral component with a retrodriver or femoral component extractor. Debride cement with hand tools or burr, using care to avoid bone fracture. If a stem is present, then remove with the appropriate extraction device. If “mismatch” exists, where femoral (or likewise, tibial) boss is smaller in diameter than the stem, creating a cement block prohibiting stem removal, remove the cement with hand tools or burr. If the stem is cemented, use hand tools, ultrasonic tools, or a burr to debride the cement. Curette and clean the canals. For tibial component removal, disrupt the prosthetic-cement/prosthetic-bone interface using an oscillating or reciprocating saw. Gently remove the tibial component with a retrodriver or tibial extractor. If stem extensions are utilised, disengage and debride all proximal cement prior to removing the stem. If stem is present, then remove stem with appropriate extraction device. If stem is grit-blasted and well-fixed, create 8mm burr holes 1.5 to 2.5cm distal to tibial tray on medial aspect and a small divot using burr, then drive implant proximally with Anspach punch. Alternatively, a tibial tubercle osteotomy may be performed. If the stem is cemented, use hand tools, ultrasonic tools or burr to debride cement

Introduction: The aim of the current investigation to study the inherent ability of biomaterial scaffolds to regenerate bone defects without osteoinductive growth factors. We have developed a biosynthetic hybrid scaffold that mimics the biofunctionality of the provisional fibrin matrix which regulated the initial stages of in vivo bone regeneration. The material is comprised of a fibrinogen backbone and polyethylene glycol (PEG) cross-links that regulate the strength, durability, and degradation of the matrix during the healing process. Precise control over the degradability of the hydrogel scaffold provides the ability to systematically regulate the cellular infiltration associated with fracture healing. Furthermore, improved physical strength (over purified native fibrin clots) enables superior handling properties and stable in situ fixation.

Materials & Methods: In the current study, a 7-mm critical size defect is created in the right tibia of female Sprague-Dawley rats (age 3–4 months); an external fixator is placed proximal and distal to the mid-section of the tibia. Pre-cast fibrinogen-PEG cylindrical hydro-gels (3-mm dia, 7-mm long) are placed into the site of the defect. Three different hydrogel compositions are tested: 1:1, 1:2, and 1:3 fibrinogen to PEG. Independent experiments demonstrate that higher concentrations of PEG give the hydrogels slower degradation kinetics. Radiographs, post operative and during follow-up, and histological evaluation were done.

Results & Discussion: Both radiography and histological evaluation reveals extensive and widespread periosteal new bone formation. Post-operative radiographs show the formation of a periosteal callus in the gap region of treated animals after five weeks compared to immediately following excision (Figure 1, right). Five weeks post-operatively, histological sections stained with H& E reveal a thick covering of newly formed and moderately differentiated lamellar-fibred bone alongside lengthy stretches of the original cortex. There are large amounts of closely packed trabeculae of recently deposited, woven-fibered bone wherever there are empty spaces of the hydrogel scaffold. These trabeculae join at their perimeters with the preexisting bone. We also demonstrate a clear relationship between the composition of the hydrogel and the synthesis of new bone in the defect site. In conclusion, we demonstrate the formation of newly synthesized bone in critical size defects in the rat tibia using a biomimetic hydrogel scaffold without the use of exogenous growth factors.

Introduction. Patellar crepitus and clunk are tendofemoral-related complications predominantly associated with posterior-stabilizing (PS) total knee arthroplasty (TKA) designs [1]. Contact between the quadriceps tendon and the femoral component can cause irritation, pain, and catching of soft-tissue within the intercondylar notch (ICN). While the incidence of tendofemoral-related pathologies has been documented for some primary TKA designs, literature describing revision TKA is sparse. Revision components require a larger boss resection to accommodate a constrained post-cam and stem/sleeve attachments, which elevates the entrance to the ICN, potentially increasing the risk of crepitus. The objective of this study was to evaluate tendofemoral contact in primary and revision TKA designs, including designs susceptible to crepitus, and newer designs which aim to address design features associated with crepitus. Methods. Six PS TKA designs were evaluated during deep knee bend using a computational model of the Kansas knee simulator (Figure 1). Prior work has demonstrated that tendofemoral contact predictions from this model can differentiate between TKA patients with patellar crepitus and matched controls [2]. Incidence of crepitus of up to 14% has been reported in Insall-Burstein® II and PFC® Sigma® designs [3]. These designs, in addition to PFC® Sigma® TC3 (revision component), were included in the analyses. Primary and revision components of newer generation designs (NexGen®, Attune® and Attune® Revision) were also included. Designs were evaluated in a patient model with normal Insall-Salvati ratio and a modified model with patellar tendon length reduced by two standard deviations (13mm) to assess worst-case patient anatomy. Results. During simulations with normal patellar tendon length, only PFC® Sigma® and PFC® Sigma® TC3 showed tendofemoral contact within the trochlea, and no design showed contact at the transition to the ICN (Figure 2). In simulations with patella baja, Insall-Burstein® II, PFC® Sigma®, and PFC® Sigma® TC3, demonstrated tendofemoral contact across the trochlea at the transition into the notch. In contrast, NexGen®, Attune® and Attune® Revision showed tendon contact for approximately half the width of the transition to the notch (Figure 3). PFC® Sigma® and Attune® demonstrated very similar tendofemoral contact to their equivalent revision components, although the shorter trochlear groove of Attune® Revision marginally increased contact at the transition. Discussion. Insall-Burstein® II, PFC® Sigma®, and PFC® Sigma® TC3 designs showed full contact with the quadriceps tendon at the anterior border of the ICN when combined with a short patellar tendon. NexGen®, Attune® and Attune® Revision had a more gradual transition between the trochlea and the notch, which resulted in less exposure to tendon contact. Even with the shorter trochlear groove required for revision components, Attune® Revision showed minimal difference in tendofemoral contact when compared with Attune®. There appears to be distinct benefit in a femoral design which reduces tendofemoral contact at the transition to the ICN; this may be of particular importance for patients with patella baja

In 2017, the British Society for Children’s Orthopaedic Surgery engaged the profession and all relevant stakeholders in two formal research prioritization processes. In this editorial, we describe the impact of this prioritization on funding, and how research in children’s orthopaedics, which was until very recently a largely unfunded and under-investigated area, is now flourishing. Establishing research priorities was a crucial step in this process.

Cite this article: Bone Joint J 2024;106-B(5):422–424.

Purpose Of The Study: Description of a new operative technique of trochleoplasty for patellar instability and its short-term results. Method: we report a new technique of trochleoplasty for Trochlear dysplasia, using Mitek anchor sutures. The purpose of the procedure is to remove the anterior femoral boss associated with Femoral Trochlear dysplasia and make the floor of the trochlea level with the anterior femoral cortex. The operation entails undermining of the trochlear and lateral condylar articular cartilage to a new corrected level where it is held with the use of No 2 Ethibond Mitek anchor sutures. These anchors are placed in the subchondral bone, suture needle passed through the articular cartilage and the sutures tied over it. Approximately 4 -5 anchor sutures are placed to hold the trochlear cartilage down to the new corrected level. This procedure can be combined with proximal and distal patellar realignment. So far, using this technique, we have operated on six patients with trochlear dysplasia and chronic patellar instability. The patients include 4 females and 2 male with an average age of 33 yrs (range 29 – 40). Average follow up is 16 months (range 8 – 24 months). There has not been any recurrence of patellar instability in the operated patients. Conclusion: Short-term follow up of a new operative technique of troachleoplasty for patellar instability shows promising results

Deltoid ligament insufficiency has been shown to decrease tibiotalar contact area and increase peak pressures within the lateral ankle mortise. Sectioning of the deltoid ligament has been shown to decrease tibiotalar contact area by 43%. This detrimental effect may create an arthritic ankle joint if left unresolved. Reconstructive efforts thus far have been less than satisfactory. Pankovich and Shivaram described the deltoid ligament as having superficial and deep components based on insertion sites. The superficial layer originates from the anterior colliculus of the medial malleolus and inserts on the navicular, calcaneus and talus. The deep layer originates from the intercollicular groove and posterior colliculus and inserts on the talus. Boss and Hintermann noted that the most consistent and strongest bands of the deltoid were the tibiocalcaneal and posterior deep tibiotalar ligaments. Chronic deltoid ligament insufficiency may be seen in several disorders including trauma and sports injuries, posterior tibial tendon disorders, prior triple arthrodesis with valgus malunion, or total ankle arthroplasty with improper component positioning or pre-existing ligament laxity. The reconstruction of the deltoid ligament in these settings may be critical to the prevention of tibiotalar arthrosis or failure of ankle prostheses from edge loading and polyethylene wear. The reconstructive technique we describe, under low torque, was able to restore eversion and external rotation stability to the talus, which was statistically similar to the native deltoid ligament. In addition, though we maximally tension this graft to give the most secure repair possible, we did not note any increased stiffness in the ankle joint through our measurement techniques. This unusual, positive secondary effect is different from that noted in studies of lateral ligament reconstruction, where ligament tensioning by all methods attempts to reproduce the native tension and not exceed it. All medial ankle ligament repairs of substance involve some type of tendon-weave (whether autograft or allograft) to achieve reconstruction. Our technique develops its strength not only from the anatomic orientation of the reconstructed ligament, but the strength of the components chosen to fix the tendon graft to the bone. The use of Endobuttons allows the entire graft to sit within the tunnels, without the potential violation of the graft ends achieved through techniques utilizing interference screw fixation. Tensioning the graft proximally through the tibia against a rigid distal construct allows greater tension to be placed on the graft at the deltoid ligament site itself than techniques which employ distal tensioning while holding the ankle into inversion. Finally, the use of a looped graft proximally secured with a post that may be moved even further proximally at the surgeon's discretion creates superior tension to achieve medial column rigidity in grossly unstable situations. Thus, given the critical importance of the deltoid ligament and the relative paucity of repair/reconstruction options available, we believe this novel approach will assist the clinician in anatomically reconstructing this challenging condition. Deltoid ligament reconstruction technique using semitendinosis allograft, with superimposed line drawing demonstrating orientation of looped graft

Introduction: In avascular necrosis [AVN] of the femoral head the dead bone undergoes osteoclastic osteolysis and is replaced by newly synthesized, immature, weak bone, which cannot withstand the daily loads. The articular surface might caves in because of these changes, and osteoarthritic joint changes can develop. Alendronate interferes with the osteoclastic activities, it can slow-down the bone turnover of the necrotic bone and can differ these changes.

The aim of this study is to delay the speedy renewal of living epiphyses by alendronate medication in order to describe the effects of it on the fate of the necrotic femoral heads in rats.

Methods: Sixty female sprague-dawley rats, 6-month old weighing about 400–500 grams, underwent surgical AVN of the right femoral heads. Forty-four rats, the treated group, were treated with alendronate 200 μgm/kg/day. Sixteen rats, the control group, were treated with saline. Both groups were daily injected subcutaneously for six weeks and sacrificed. Both femoral heads were harvested and were evaluated microscopically and stained by H& E.

Results: The necrotic femoral heads of the control group, which were not treated by alendronate, were severely distorted with osteoarthrosis features as; collapse of the epiphysis, pannus formation, filling of spaces by chronically and mildly inflamed densely textured fibrous tissue which was polluted by numerous tiny particles of necrotic bone. Additionally, large chunks of necrotic articular cartilage were haphazardly scattered in the fibrous tissue. All hematopoietic and fat cells of the intertrabecular spaces of the epiphysis were replaced by fibrous tissue. More often than not, the cartilage of the physis was focally or entirely absent such that osseous trabeculae of the epiphysis and metaphysis linked with each other, forming so-called epiphyseal-metaphyseal bridges. The above described alterations were encountered in all animals, yet their severity varied.

The decisive difference between the necrotic femoral heads of otherwise untreated in opposition to the alendronate-medicated rats was the preservation of a hemispherical configuration of the femoral heads. There was no distortion of the femoral heads in the alendronate-treated animals and the femoral heads preserved their roundness.

All femoral heads of the non-operated left hips were microscopically normal.

Discussion: It has become clear that the degree of architectural distortion of the femoral epiphyses depends on the extent of bone turnover leading to resorption of all debris and its replacement by living osseous and soft tissues. The more rapidly and more extensively the reconstruction of living epiphyses progresses, the smaller is the prospect of reshaping a hemispherical or near-hemispherical femoral head. The recently rebuilt epiphyses cannot carry daily transarticular loads without caving in. The revascularization-related reconstitution of weak bony trabeculae is blamed for the collapse of the femoral heads. If this indeed is the case, the remodeling of the necrotic femoral heads should be delayed, rather than sped-up. Alendronate interferes with the osteoclastic activities and hence, slowing-down the bone turnover.

The osteoclastic activity is detrimental for the conservation of a hemispherical femoral head because of the rapidly occurring replacement of the necrotic bone by living tissues. Halting the activities of the osteoclasts by a biphosphonate would stop the hasty osteoneogenesis, which is responsible for the early femoral capital disfigurement and might delay the regeneration of osteo-arthiritic changes of the joint later on.

Objectives

The primary stability of the cementless Oxford Unicompartmental Knee Replacement (OUKR) relies on interference fit (or press fit). Insufficient interference may cause implant loosening, whilst excessive interference could cause bone damage and fracture.

The aim of this study was to identify the optimal interference fit by measuring the force required to seat the tibial component of the cementless OUKR (push-in force) and the force required to remove the component (pull-out force).