Towards a solution of the wires' slippage problem of the Ilizarov external fixator.

Clinical experience has indicated that many complications during treatment with the Ilizarov method, and mainly tract infection, are related to decreased wire tension. The aim of this work was to evaluate biomechanically a novel wire tensioning and clamping system that will minimise or even diminish the reduction of the wire pretension during treatment. The proposed approach is based on threading of the wire end in a sufficient length. The wire pretension is applied by twisting a nut on the threaded part of the wires against the ring and is recorded by an incorporated force sensor. For biomechanical evaluation, the frame, consisting of a polyethylene bar, simulating the bone fragment, suspended on two rings, was subjected to a dynamic load of 0-800 N at a frequency of 0.5 Hz. After dynamic loading for 20 min, loss of the initial wire pretension for the novel clamping system ranged between 12 and 16%. The average loss for conventionally clamped wires was 75%. The advantages of the novel clamping system were the much greater ability to sustain the transverse load and the easy and effectual wire re-tensioning. Although wire slippage has been avoided with the novel system, wire material yield is still responsible for a pretension loss.

The role of oligodendrocytes in the molecular pathobiology and potential molecular treatment of cervical spondylotic myelopathy.

Cervical spondylotic myelopathy (CSM) is a very common and debilitating disease; however, its underlying pathocellular process remains uncertain. Attempts have been made to reproduce CSM in experimental animal models in order to deepen the knowledge on the molecular pathobiology of this disease. The up-to-date observations have established the apoptosis of oligodendrocytes (OLGs) as the principal pathocellular process of CSM. Since favorable neurological recovery cannot be obtained in afflicted patients, even after the decompression surgery, elucidation of the apoptotic cascade in OLGs may unveil possible molecular treatments which could inhibit demyelination and ameliorate the neurological deficits. Moreover, additional therapeutic benefits may include improvement of myelin self-repair capability by stimulating OLG progenitor cells to become mature and finally, myelinating OLGs. This review focuses on the factors and mechanisms of crucial importance for developing antiapoptotic treatments. Critical evaluations of the role of OLGs in molecular pathobiology of CSM as well as strategies for potential remyelination of CSM are also provided. The analyses and evaluations of the experimental findings can possibly lead to treatment of CSM as well as to development of novel biopharmacenticals.

Vibrational bone characteristics versus bone density for the assessment of osteoporosis in ovariectomized rats.

Our previous research findings suggested this integrated study in order to monitor changes of bone properties and assess bone integrity using vibrational characteristics in osteoporosis. The method is based on measurement of the bone dynamic characteristic modal damping factor (MDF). The experimental animal model is ovariectomized rat followed by alendronate treatment. According to the experimental design, adult female Wistar rats are ovariectomized and 60 days later, with confirmed osteoporosis, the population is divided into two groups. One is administered alendronate and the second is given no treatment. Furthermore, established techniques such as pQCT and histomorphometry are applied at all time points, in order to compare and correlate to MDF. The results indicate induction of osteoporosis due to ovariectomy and render MDF capable of monitoring changes in bone material properties and architecture, with high sensitivity and repeatability.

SAPHO Syndrome Diagnosis and Treatment: Report of Five Cases and Review of the Literature.

BACKGROUND: The term "SAPHO (Synovitis, Acne, Pustulosis, Hyperostosis and Osteitis) syndrome" includes a variety of musculoskeletal disorders associated with skin conditions; Osteitis is the most prominent skeletal lesion, whereas palmoplantar pustulosis and acne are the main skin lesions. Diagnosing SAPHO syndrome is difficult, because this syndrome is often confused with suppurative osteomyelitis, which has similar clinical and pathologic findings. SAPHO diagnosis is even more difficult when atypical sites are involved and there are no skin lesions. PATIENTS AND METHODS: This case series presents five patients (3 women, 2 men), ages 27 to 44 years, who came to the Orthopaedic Department outpatient clinic for evaluation of pain in the humerus, clavicle, sacroiliac joints, and/or distal radius, and were diagnosed with SAPHO syndrome. Clinical and radiologic findings, treatment and outcome data, with up to 4 years of follow-up are presented. An extensive discussion of the clinical presentation, published literature, treatment options and outcome of SAPHO syndrome is also included. RESULTS: Once the diagnosis of SAPHO syndrome was established, treatment with antibiotics (clindamycin) and non steroid anti-inflammatory drugs (lornoxicam) was remarkably effective. All patients did well and remained symptom free for up to four years, after a 3-8 month course of treatment. INTERPRETATION: SAPHO syndrome should be included in the differential diagnosis when evaluating patients with lytic, sclerotic, or hyperostotic bone lesions and pain. Prompt SAPHO syndrome recognition, followed by appropriate therapy with antibiotics and NSAIDs can produce rapid symptom resolution, while avoiding unnecessary procedures and longterm antibiotic therapy.

Complications of anterior surgery in cervical spine trauma: an overview.

OBJECTIVE: Although anterior surgery for cervical spine injuries is a widespread procedure, articles regarding its overall complications are infrequently published in the literature. In the current study we focus on the complications encountered after anterior instrumented stabilization of cervical spine injuries and we discuss ways to minimize them. PATIENTS AND METHODS: Patients with unstable lower cervical spine injuries who underwent anterior surgery over a 15-year period were identified and 74 patients with adequate follow-up were included in the study. Indication for surgery was set by the instability criteria of White and Panjabi. Demographic information, initial neurological examination, surgical reports, imaging findings and follow-up records were evaluated. RESULTS: Complications were classified as intraoperative (technique-related) and postoperative. Although radiological "complications" were noted, they had no or minor clinical consequences for the patient. We identified 9 patients with clinically significant complications: no purchase of the screws, late angulation deformity, screw breakage, backout of the screws and postoperative hematoma. Overall, 3 out of 74 patients (4%) were reoperated due to significant screw backout causing dysphagia, no purchase of the screws being completely in the adjacent disc and screw breakage, respectively. CONCLUSION: Anterior surgery for cervical spine injuries can present several complications, yet the technique is in a way permissive, even during the learning curve. Considering the significant morbidity of these patients, the reported rate of clinically significant complications is considered acceptable, and it could be further minimized by good preoperative planning, careful surgical technique and the use of modern implants and instrumentation.

Anatomical study and colour Doppler assessment of the skin perforators of the anterior tibial artery and possible clinical applications.

BACKGROUND: Traumatic or trophic defects of the soft tissue of the lower leg are quite often very difficult to manage, especially in the distal third of the leg. Fasciocutaneous flaps are a relatively simple option for covering small- and medium-sized defects of the lower leg. The aim of this study is to investigate the distribution of septocutaneous perforators of the anterior tibial artery and their possible clinical applications. METHODS: An anatomical study was performed on 50 fresh adult cadaveric lower extremities. Using coloured contrast materials, the location of septocutaneous perforators, originating from the anterior tibial artery, were mapped. These findings were then compared with colour Doppler imaging (CDI) data in 20 living volunteers. RESULTS: The septocutaneous perforators of the anterior tibial artery follow a reproducible pattern all over the lower leg (septa I, II and III). In the distal segment, we found relatively few perforators. There was a marginal difference between cadaveric and CDI data for perforators with diameter >or=1mm. The average number of anterior tibial artery septocutaneous perforators in anatomical dissections was 6.6+/-2.4, while CDI revealed 8.2+/-3.2 perforators in living volunteers (P=0.053). In five areas of the lower leg, there is a >50% chance that a septocutaneous perforator with diameter >or=1mm is coming off the anterior tibial artery. Anatomical dissections for a cutaneous territory 5 cm above the lateral maleollus, and 10 cm in width, revealed 6.1+/-2.2 septocutaneous perforators (range 4 to 12). CONCLUSIONS: CDI, paired with knowledge of anatomical details, is a reliable tool for preoperative identification of septocutaneous perforators of 1mm or larger outer diameter, thus providing critical information for planning and harvesting safe fasciocutaneous flaps of the lower leg. Additionally, according to our anatomical study, a new transverse fasciocutaneous flap (Type B according to the Nahai-Mathes classification), located over the distal anterolateral third of the lower leg and based on perforators of the anterior tibial artery, may be successfully used for covering selected defects of the distal third of the lower leg.

The effect of nifedipine on the patency of microvascular anastomosis in rats.

Despite advances in microsurgical technique and experience in clinical microvascular surgery, there remains the possibility of vessel thrombosis. Factors that may contribute to vascular pedicle thrombosis include operative trauma, pedicle malposition, kinking, hypercoagulability and arterial vasoconstriction. The purpose of this study was to evaluate the effect of intravenous administration of nifedipine on the patency of the microvascular anastomosis of the femoral artery in rats. A total of 60 rats were used and divided into three groups. The first group (A) was used as a control group with no medical agent, the second group (B) was medicated with heparin, and the third group (C) was medicated with nifedipine. Patency was assessed with the distal empty refill test, one hour (1) and forty-eight hours (48) after completion of the anastomosis. The nifedipine and heparin treated groups (B & C) did not show higher patency rate compared to the control group (A). There was no statistically significant difference of patency percent after 1 hour and 48 hours among the three groups (p = 0.231/p = 0.480). Intravenous administration of nifedipine does not improve the patency of microvascular anastomosis. Surgical technique remains the most important factor for successful microvascular anastomosis.

A morphological index for assessing hip osteoarthritis severity from radiographic images.

A new method is proposed for assessing the severity of hip osteoarthritis (OA) based on radiographic hip joint space (HJS) morphology. 64 hips of patients with verified unilateral OA or bilateral OA were studied by digitizing the corresponding pelvic radiographs. Radiographic OA severity was assessed employing the Kellgren and Lawrence (KL) scale. Using custom-developed software, radiographs were enhanced, the margins of both HJSs were outlined, and 64 regions of interest (ROIs), corresponding to the delineated HJSs, were obtained. Employing custom-developed algorithms, an index ("joint space morphological index" - JSMI) evaluating alterations in the shape and size of HJS was introduced, calculated and normalized with respect to each patient's individual anatomy. The JSMI values were used to introduce classification rules concerning the characterization of a hip in accordance with the KL scale. For each patient in the unilateral OA group, the OA severity was expressed as the percentage of the HJS area difference between the patient's osteoarthritic and contralateral normal hip. The per cent HJS area difference and the JSMI values were used in the design of a regression model for providing a quantitative estimation of OA severity. The per cent HJS area difference correlated highly with the pathological JSMI values (r = -0.83, p<0.001). The implementation of the JSMI-based classification rules resulted in high classification accuracies for characterizing hips as normal or osteoarthritic, 90.6% (95% exact confidence interval (CI): 80.7-96.5%), as well as for discriminating among OA severity categories, 91.7% (95% CI: 77.5-98.2%). Additionally, a simplified approach of JSMI calculation is suggested for daily clinical use. These JSMI values (JSMI simplified) were found not to differ significantly from (p>0.05), and to be strongly correlated with (r = 0.96, p<0.001), the corresponding ones obtained by the computerized approach. Additionally, the implementation of classification rules based on JSMI simplified resulted in classification accuracies identical to the corresponding ones obtained for the JSMI-based rules. The proposed method may be utilized for evaluating OA and monitoring OA progression.

Gamma nail breakage: a report of four cases.

Gamma nails have been used extensively for the treatment of proximal femoral fractures. Nail breakage at the level of the aperture of the lag screw is rare. We report 4 such cases mainly associated with a large posteromedial cortex gap and nonunion. The need for adequate reduction to avoid such a complication is emphasised.

Assessing hip osteoarthritis severity utilizing a probabilistic neural network based classification scheme.

A computer-based classification system is proposed for the characterization of hips from pelvic radiographs as normal or osteoarthritic and for the discrimination among various grades of osteoarthritis (OA) severity. Pelvic radiographs of 18 patients with verified unilateral hip OA were evaluated by three experienced physicians, who assessed OA severity employing the Kellgren and Lawrence scale as: normal, mild/moderate and severe. Five run-length, 75 Laws' and 5 novel textural features were extracted from the digitized radiographic images of each patient's osteoarthritic and contralateral normal hip joint spaces (HJSs). Each one of the three sets of textural features (run-lengths, Laws' and novel features) was separately utilized for assigning hips into the three OA severity categories, by means of a probabilistic neural network (PNN) classifier based hierarchical tree structure. The highest classification accuracy (100%) for characterizing hips as normal, of mild/moderate or of severe OA was obtained for the novel textural features set. Additionally, the novel textural features were used to design a mathematical regression model for providing a quantitative estimation of OA severity. Measured OA severity values, as expressed by HJS-narrowing, correlated highly (r=0.85, p<0.001) with the predicted values by the mathematical regression model. The proposed system may be valuable in OA-patient management.

In vitro effects of non-steroidal anti-inflammatory drugs on cytokine, prostanoid and matrix metalloproteinase production by interface membranes from loose hip or knee endoprostheses.

OBJECTIVE: To study the effects of the non-steroidal anti-inflammatory drugs (NSAIDs) aceclofenac, piroxicam, tenoxicam and indomethacin on cytokine, matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs) and prostaglandin E2 (PGE2) production, by interface membranes (IFT), obtained at revision surgery for aseptic loosening of total joint arthroplasty. Involvement of these soluble factors is well documented and probably, a pharmaceutically induced inhibition of them might retard loosening. METHODS: IFTs from 10 patients with a loose hip or knee endoprosthesis were collected. The possibility of septic loosening was thoroughly excluded by histopathologic and microbiologic evaluation. IFTs were cultured in the absence or presence of the tested drugs and the levels of the soluble mediators were determined, using electrophoretic and enzyme-linked immunosorbent assay techniques. Paracetamol was used as neutral drug. RESULTS: All NSAIDs exhibited a pronounced inhibitory effect upon the production of interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-alpha). This specific effect on IL-6 is reported in the literature for the first time. The majority of NSAIDs also induced the production of IL-1beta in an adequate portion of samples. These drugs did not have a clear effect on MMP synthesis, but they had a stimulatory tendency on TIMP-1 production. Paracetamol, significantly decreased the synthesis of TNF-alpha and that of the gelatinases. CONCLUSION: Our in vitro results are encouraging, since it appears that the action of NSAIDs, globally considered, may be beneficial upon the loosening process. The inhibitory effect of paracetamol upon TNF-alpha and gelatinases is intriguing. Our data, if supported by similar observations, probably justify performance of long-term clinical trials.

Osteoarthritis severity of the hip by computer-aided grading of radiographic images.

A computer-aided classification system was developed for the assessment of the severity of hip osteoarthritis (OA). Sixty-four radiographic images of normal and osteoarthritic hips were digitized and enhanced. Employing the Kellgren and Lawrence scale, the hips were grouped by three experienced orthopaedists into three OA-severity categories: Normal, Mild/Moderate and Severe. Utilizing custom-developed software, 64 ROIs corresponding to the radiographic Hip Joint Spaces were manually segmented and novel textural features were generated. These features were used in the design of a two-level classification scheme for characterizing hips as normal or osteoarthritic (1st level) and as of Mild/Moderate or Severe OA (2nd level). At each classification level, an ensemble of three classifiers was implemented. The proposed classification scheme discriminated correctly all normal hips from osteoarthritic hips (100% accuracy), while the discrimination accuracy between Mild/Moderate and Severe osteoarthritic hips was 95.7%. The proposed system could be used as a diagnosis decision-supporting tool.

Intramedullary knee arthrodesis as a salvage procedure after failed total knee replacement.

Septic and aseptic loosening with or without extensive bone loss after total knee replacement are the most common indications for knee fusion. Both external fixation and intramedullary nailing can be used for the treatment, though the latter appears to be the method of choice for most patients. Nine patients were treated after a total knee replacement failure using intramedullary nailing. A long intramedullary nail with a proximal interlocking screw was used in five cases, and a customised nail was used in four cases. Successful fusion occurred in eight of nine patients (89%). Average time for the joint union was 6.5 months, and average operative blood loss was 860 ml. In two patients, iliac crest and patellar bone graft were also used. In conclusion, intramedullary nailing can give excellent results in achieving knee fusion after a failed knee replacement as it allows early weight bearing and at the same time offers stability, pain relief, and a high rate of union, even though the surgical technique is demanding.

Quantitative assessment of hip osteoarthritis based on image texture analysis.

A non-invasive method was developed to investigate the potential capacity of digital image texture analysis in evaluating the severity of hip osteoarthritis (OA) and in monitoring its progression. 19 textural features evaluating patterns of pixel intensity fluctuations were extracted from 64 images of radiographic hip joint spaces (HJS), corresponding to 32 patients with verified unilateral or bilateral OA. Images were enhanced employing custom developed software for the delineation of the articular margins on digitized pelvic radiographs. The severity of OA for each patient was assessed by expert orthopaedists employing the Kellgren and Lawrence (KL) scale. Additionally, an index expressing HJS-narrowing was computed considering patients from the unilateral OA-group. A textural feature that quantified pixel distribution non-uniformity (grey level non-uniformity, GLNU) demonstrated the strongest correlation with the HJS-narrowing index among all extracted features and utilized in further analysis. Classification rules employing GLNU feature were introduced to characterize a hip as normal or osteoarthritic and to assign it to one of three severity categories, formed in accordance with the KL scale. Application of the proposed rules resulted in relatively high classification accuracies in characterizing a hip as normal or osteoarthritic (90.6%) and in assigning it to the correct KL scale category (88.9%). Furthermore, the strong correlation between the HJS-narrowing index and the pathological GLNU (r = -0.9, p<0.001) was utilized to provide percentages quantifying hip OA-severity. Texture analysis may contribute in the quantitative assessment of OA-severity, in the monitoring of OA-progression and in the evaluation of a chondroprotective therapy.

Evaluation of modal damping factor as a diagnostic tool for osteoporosis and its relation with serum osteocalcin and collagen I N-telopeptide for monitoring the efficacy of alendronate in ovariectomized rats.

Osteoporosis is a metabolic bone disease characterized by reduced bone mass and deterioration of bone microarchitecture. It results from the shift of the osteoblast-osteoclast activity equilibrium in favor of the later. Although, a number of biochemical markers, such as collagen I N-telopeptide (NTx) and osteocalcin (OC), have been used for monitoring bone remodeling, a new, monitoring, non-invasive method, which is based on the measurement of the dynamic characteristic of bone and is known as modal damping factor (MDF), has not been evaluated as a diagnostic tool for osteoporosis. Bisphosphonates, such as alendronate, have an established role in the treatment of osteoporosis. The aim of the present study was, therefore, to evaluate the effects of alendronate on the levels of MDF, serum NTx and OC on osteoporosis induced by ovariectomy in rats. Furthermore, the effects of alendronate on osteoporosis have been histologically evaluated. Fifteen adult female Wistar rats were bilaterally ovariectomized and osteoporosis was histologically confirmed and by the use of peripheral quantitative computerized tomography (pQCT). MDF was applied to assess the bone structural integrity. The serum levels of NTx (37.4+/-0.5 nM bone collagen equivalents, BCE) and OC (111.0+/-8.2 ng/mL) were found to significantly increase following ovariectomy (72.0+/-2.9 nM BCE and 213.5+/-12.1 ng/mL, respectively, p<0.001). As assessed by histology and the levels of NTx and OC in sera, animals treated with alendronate presented a statistically significant deceleration in the progression of the disease in comparison to the no-therapy control group (alendronate group NTx levels: 146.3+/-8.9 nM BCE versus no-therapy control group NTx levels: 265.3+/-14.0 nM BCE, p<0.001, alendronate group OC levels: 205.6+/-18.2 ng/mL versus no-therapy group OC levels: 353.9+/-26.1 ng/mL, p<0.001). Data obtained from the vibration analysis performed illustrated that the change in damping was equal or greater to the change in total and trabecular density, respectively. Damping increased with decreasing bone density, as expected, given that damping accounts for the structural integrity of bone (MDF value before ovariectomy: 0.058+/-0.003 versus MDF value after ovariectomy: 0.098+/-0.003, p<0.001). The higher damping values correspond to more deteriorated structures. In particular, both total and trabecular density were significantly decreased following ovariectomy (total density before ovariectomy: 702.4+/-19.0 versus total density after ovariectomy: 542.2+/-12.8, p<0.001, trabecular density before ovariectomy: 445.3+/-13.0 versus trabecular density after ovariectomy: 396.7+/-8.4, p<0.05). MDF value of the alendronate group (0.07+/-0.002) was significantly lower (p<0.001) as compared to MDF value after ovariectomy (0.098+/-0.003) and that of the no-therapy group (0.1+/-0.004, p<0.001). The administration of alendronate seemed to have no effect on either total or trabecular density, since both parameters continued to decrease (alendronate group total density: 549.4+/-12.3, alendronate group trabecular density: 368.4+/-14.7). However, when this was compared to the no-therapy group, a statistically significant difference of total density at the 0.05 level was observed (no-therapy total density: 464.8+/-9.1). The results of this study suggest that combined measurements of MDF, NTx and OC may be a potential diagnostic tool for osteoporosis and monitoring bone integrity during treatment with bisphosphonates. Furthermore, administration of alendronate showed to offer a critical deceleration in the progression of osteoporosis.

The use of the Ilizarov method as a salvage procedure in infected nonunion of the distal femur with bone loss.

We reviewed 13 patients with infected nonunion of the distal femur and bone loss, who had been treated by radical surgical debridement and the application of an Ilizarov external fixator. All had severely restricted movement of the knee and a mean of 3.1 previous operations. The mean length of the bony defect was 8.3 cm and no patient was able to bear weight. The mean external fixation time was 309.8 days. According to Paley's grading system, eight patients had an excellent clinical and radiological result and seven excellent and good functional results. Bony union, the ability to bear weight fully, and resolution of the infection were achieved in all the patients. The external fixation time was increased when the definitive treatment started six months or more after the initial trauma, the patient had been subjected to more than four previous operations and the initial operation had been open reduction and internal fixation.

Correlation between radiological parameters and patient-rated wrist dysfunction following fractures of the distal radius.

The present study investigates the correlation between radiological parameters of wrist fractures and the clinical outcome expressed by objective clinical parameters and the level of patient-rated wrist dysfunction. Thirty consecutive cases of unstable distal radial fractures treated with closed reduction and percutaneous fixation were prospectively studied for a period of one year. The outcome parameters included objective clinical and radiological parameters and the previously described and validated patient-rated wrist evaluation (PRWE) score. Analysis showed that for unstable (AO classification types 23-A2, -A3, -C1 and -C2) fractures the fracture type affects the range of wrist palmarflexion (p=0.04) and that the presence of postoperative articular 'step-off' affects the range of wrist dorsiflexion and the patient-rated wrist function at the final time of the study (p<0.01 and p=0.02, respectively). It is also shown that permanent radial shortening and loss of the palmar angle were associated with prolonged wrist pain (p<0.01 and p=0.03, respectively). Our finding that residual articular incongruity correlates with persisting loss of wrist dorsiflexion and wrist dysfunction contradicts the view that loss of articular congruity is associated with late development of articular degeneration but not with early wrist dysfunction. Additionally, this study failed to show any association between the fracture type and the functional outcome as rated by the patients.

Impact energy absorption by specimens from the upper end of the human femur.

A cadaveric biomechanical study was performed to investigate the fracture energy absorbed by strips of bone from the proximal femur in relation to age and gender, under impact loading conditions. Four groups (young male, young female, old male, old female) of four cadaveric proximal femurs were used in each case. Four bone strips were taken from the neck and four from the subtrochanteric area and these were tested under dynamic-impact conditions using the Charpy impact test. The fracture energy was calculated as the energy needed to achieve fracture per unit area, and expressed in J/m2. Bone specimens from young males are significantly tougher under impact conditions to those of females (p = 0.001), whereas between the old male and female groups, fracture energy does not significantly differ (p = 0.165). There was also significant difference (p < 0.0005) between the young and the old groups in both genders. The fracture energy absorption of the subtrochanteric area compared to that of the femoral neck for the same group of age and gender is in general slightly higher for all groups. In conclusion, gender in the young age group played a significant role in bone resistance in breaking whereas in the older age group it played a less important role.

Viscoelastic properties of cartilage-subchondral bone complex in osteoarthritis.

OBJECTIVE: This study examines viscoelastic properties of the 'unaffected' tibial condyle in unicompartmental osteoarthritic knees, in order to determine whether to preserve it or not in knee replacement operations. DESIGN: The viscoelastic properties of longitudinal strips of cartilage and subchondral bone from osteoarthritic and healthy knees were studied. METHODS: Nine medial compartment osteoarthritic and nine cadaveric knees, all age- and gender-matched, were studied. Samples from polyethylene and methacrylate cement were also obtained and all then tested in the DMA (Dynamic Mechanical Analysis) testing apparatus. The dynamic modulus of elasticity (E(dyn)) and the loss factor (tan delta) were measured. RESULTS: The medial compartment in osteoarthritic knees had lost its viscoelastic properties, having a significantly higher E(dyn) compared to the lateral one, and lower values of loss factor. In healthy knees there was no significant difference (p=0.18) in viscoelastic properties between both compartments and with the unaffected side of the osteoarthritic knee. Polyethylene and cement appear to have a high modulus of elasticity compared to both the healthy and the osteoarthritic knees. CONCLUSIONS: The 'unaffected' (lateral) tibial condyles in medial compartment osteoarthritic knees seem to preserve their viscoelastic properties; it is worth considering a hemiarthroplasty. The significant modulus of elasticity difference between the condyles-polyethylene-cement results in different deformation in the interface between them and induces micromotion and loosening.