[Discrepancy between radiographic and true cup position after total hip arthroplasty : Are we interpreting our radiographic quality indicators correctly? Video article]. / Diskrepanz zwischen radiographischer und tatsächlicher Pfannenstellung bei der Hüft-TEP-Versorgung : Interpretieren wir unsere radiologischen Qualitätsindikatoren richtig? Videobeitrag.

BACKGROUND: After total hip arthroplasty (THA), objective postoperative quality control is done via X­rays by as component position assessment. The cup position is defined by its version and inclination. However, there is a discrepancy between radiographically measured and true (anatomic) cup position, which may lead to misinterpretation. METHODS: To visualize the discrepancy between true and radiographically measured cup position, in this video, a cup holder was used to set the angular cup version and inclination. Hereby, the cup position (anteversion and inclination) can be characterized in its radiographic and anatomic definition in greater detail. The viewer of this video should receive an impression as to when radiographically measured cup angles must be considered with caution. RESULTS: In a simultaneous X­ray and image sequence, this video shows decreased radiographic inclination measurement with increasing anterior rotation of the cup exceeding 20° of anteversion, yet with unchanged true inclination on the cup holder. Isolated consideration of the radiographic angles of anteversion and inclination may cause misinterpretation of true cup position. In pectoral illustration we show that variations in cup version and inclination may remain undetected when considering isolated the radiographic cup parameters. CONCLUSION: True cup position in its anatomical definition can be calculated from the radiographically measured position. For this purpose, both cup parameters (radiographic anteversion and radiographic inclination) have to be taken into account.

[Rheumatism operations in a state of flux-"Foot"]. / Rheumaoperationen im Wandel ­ "Fuß".

Surgical management of rheumatic feet has dramatically changed over the last decades influenced by the development of new pharmacological drugs and tissue-preserving surgical procedures. It has switched from joint resection to joint-sparing procedures as the method of choice. Nevertheless, the surgical interventions commonly used for non-rheumatic patients cannot be applied to rheumatic patients without reflection: in addition to the basic treatment, comorbidities, degree of mobilization of the patient, orthopedic shoe engineering and orthotic treatment play a major role. Due to the decreasing incidence of the classical rheumatic foot, it has become even more important for physicians, physiotherapists and ergotherapists to recognize the development of such a disease as early as possible and immediately start the appropriate treatment.

[The knee joint in rheumatoid arthritis-current orthopaedic surgical treatment options]. / Kniegelenk bei rheumatoider Arthritis ­ aktuelle orthopädisch-chirurgische Therapieoptionen.

The knee joint is often involved in rheumatoid arthritis. Despite ever-improving medical antirheumatic therapies, surgical treatment continues to play an important role in optimal multidisciplinary care. The aim of the present work is to process current orthopedic surgical therapy procedures on the knee joint according to disease stage. In the early phase, joint-preserving arthroscopic procedures for synovectomy are used. In advanced joint destruction, joint function can be restored by total knee arthroplasty. Of central importance for optimal patient care are individual treatment and good interdisciplinary coordination of all involved specialist groups.

What is the optimal valgus pre-set for intramedullary femoral alignment rods in total knee arthroplasty?

PURPOSE: In total knee arthroplasty (TKA), intramedullary guides are often used for aligning the distal femoral cutting block. Because of the highly varying angles between the mechanical axis and the anatomical femoral axis (AMA), different valgus pre-sets have been recommended. The present study investigated the optimal valgus pre-set (measuring the AMA in long-leg radiographs or at 5°, 6°, 7° or 8° valgus) to align the cutting block perpendicularly to the mechanical axis. METHODS: The AMA was preoperatively measured in weight-bearing long-leg radiographs. After alignment of the cutting block by means of an intramedullary rod, deviation of the block from the mechanical femoral axis was measured with a pinless navigation device. The true AMA (tAMA) was calculated by adding the valgus pre-set of the alignment rod to the deviation measured with the navigation device. Mean deviations between the tAMA and (a) the AMA measured by the surgeon, (b) the AMA calculated with the computer software, (c) 5°, (d) 6°, (e) 7° and (f) 8° valgus pre-sets were measured for each patient. The lowest mean differences were determined. RESULTS: The 40 knees measured showed a mean tAMA of 7.2° valgus (1.7 SD) (range 4°-11.5°). The following mean differences and 95 % limits of agreement were calculated: 2.2 (-1.2, 5.5) to the tAMA for the 5° valgus pre-set, 1.2 (-2.2, 4.5) for 6°, 0.2 (-3.2, 3.5) for 7° and -0.8 (-4.2, 2.5) for 8°. AMA measurements by the surgeon and with the digital medical planning software yielded mean differences of 0.6 (-3.1, 4.3) and 0.4 (-4.1, 4.8), respectively. CONCLUSION: In the present setting, the best mean distal femoral cutting block alignment perpendicular to the mechanical femoral axis could be achieved with a valgus pre-set of 7° and not by measuring the AMA. Nevertheless, we recommend conducting weight-bearing radiographs of the entire leg prior to TKA for easy detection of any anatomical varieties, old fractures, long stems of total hip arthroplasties or cement. However, surgeons must be aware that exact coronal component alignment can only be achieved by navigational devices. LEVEL OF EVIDENCE: Diagnostic study, Level II.

[Prevention of periprosthetic joint infections : Not evidence-based strategies]. / Vermeidung periprothetischer Infektionen : Nicht evidenzbasierte Maßnahmen.

BACKGROUND: Surgical site infections are the most common nosocomial infections in orthopedic surgery. Strategies to prevent these infections are of enormous relevance. OBJECTIVES: Evidence-based procedures such as hand disinfection, prophylactic antibiotic application, hair removal with electric clippers, or preoperative treatment of Staphyloccus aureus are listed in national and international guidelines. Beside these measures, several scientifically not confirmed methods, e.g., the administration of antibiotic prophylaxis for several days or the usage of helmets during surgery, are still practiced. These measures are not evidence-based and should not be performed anymore. CONCLUSION: Only the consequent implementation of evidence-based procedures can help prevent surgical site infections.

[Denervation of the patella: influence on mid-term results after total knee arthroplasty]. / Retropatellare Denervierung : Einfluss auf die mittelfristigen Ergebnisse von Knietotalendoprothesenimplantationen.

BACKGROUND: The purpose of the study was to determine possible differences in the mid-term results of total knee arthroplasty in patients treated with and without denervation of the patella. PATIENTS AND METHODS: This study included 80 total knee replacements in 71 patients who were treated with total knee replacement, either with (n = 40) or without (n = 40) simultaneous denervation of the patella out of a total population with 122 knee replacements in 100 patients. Comparability of both groups was achieved by applying matching criteria. All patients were reviewed by isokinetic tests, physical and radiological examination. The mean follow-up time was 2.2 years. RESULTS: The mean hospital for special surgery (HSS) score revealed no statistically significant differences between both groups (with denervation 77.9 ± 11.1 and without denervation 77.8 ± 11.0, p = 0.976). The isokinetic torque measurements with low angle velocity (60°/s) indicated slightly higher values during extension (60.2 ± 32.2 Nm versus 55.8 ± 25.2 Nm, p = 0.497) and flexion (52.4 ± 28.3 Nm versus 46.1 ± 22.3 Nm, p = 0.272) movements of the affected knee joint. However, the differences did not reach statistical significance. At high angle velocity (180°/s) no differences could be found between both groups. No cases of postoperative necrosis of the patella were observed. Anterior knee pain after denervation was reported in 6 cases (15 %) compared to 10 cases (25 %) in patients who were treated without denervation (p = 0.402). CONCLUSION: No statistically significant differences could be found between patients with and without denervation of the patella for total knee arthroplasty.

No difference in accuracy between pinless and conventional computer-assisted surgery in total knee arthroplasty.

PURPOSE: Many studies have demonstrated higher precision and better radiological results in Total knee arthroplasty (TKA) with computer-assisted surgery (CAS). On the other hand, studies revealed a lengthening of operation time up to 20 min for this technique and demonstrated rare additional complications as fractures and neurovascular injuries caused by the array pins and any intraoperative array dislocation leads to abortion of CAS. To combine the advantages and eliminate the disadvantages of standard CAS, we evaluated the accuracy of a so-called pinless CT-free version of knee navigation (pinless CAS) abandoning the reference pins and reducing the necessary workflow to a minimum. METHOD: The present study compares the accuracy of the reference methods of two different CT-free knee navigation software versions (Brainlab Knee 2.1 and Brainlab Knee Express 2.5). Thirty patients received TKA assisted by standard CAS. Intraoperatively, the proposed bony resections of standard CAS were matched with the new pinless CAS. Postoperatively, the results were checked by evaluating the radiographs concerning leg axis, femoral flexion and tibial slope. RESULTS: All results concerning precise cuts (femoral as well as tibial coronal/varus-valgus alignment, femoral flexion alignment and tibial slope, resection height) were comparable between both groups (n.s.). In femoral, we found a mean deviation of coronal alignment of 0.3° (SD 0.7) and flexion of 0.2° (SD 0.8). In tibial, we found a mean deviation of coronal alignment of 0.2° (SD 0.5) and slope of 0.2° (SD 0.6). The mean additional operation time for the pinless CAS was below 2 min. The postoperative mechanical leg axis was within the threshold of 3° in all patients, tibial slope and femoral flexion matched with CAS values. CONCLUSION: In clinical routine, pinless CAS can comprise the advantages of CAS leaving the disadvantages aside. It reduces surgical time and avoids complications associated with the tracking pins of conventional CAS.

[Bone marrow edema syndrome (BMES)]. / Das Knochenmarködemsyndrom (KMÖS).

Bone marrow edema (BME) syndrome represents a pathologic accumulation of interstitial fluid in bone - with a traumatic BME being differentiated from a non-traumatic, often ischemic, and a reactive as well as a mechanical BME. Atraumatic/ischemic BME is inconsistently described as a separate entity or as a reversible preliminary stage of osteonecrosis (ON). However, there is always the risk of transformation of BME into ON and subsequent joint destruction. The most common sites of BME are the hip, knee, and ankle. Magnetic resonance imaging is the diagnostic gold standard. Differential diagnoses of the transient BME as osteonecrosis, osteochondrosis dissecans, and a reflex dystrophy should be considered. Conservative or surgical treatment is considered, depending on the etiology of BME. BME syndrome is generally treated conservatively. Infusion of prostacycline or bisphosphonates is a promising option. Ischemic BME and early stages of ON can be successfully treated by core decompression. A combination of both treatment options may also offer advantages.

The impact of chemical synovectomy with sodium morrhuate on human chondrocytes and cartilage in vitro.

The vessel sclerosing property of sodium morrhuate is useful in treatment of recurrent joint effusions particularly in cases of knee joint effusions. It also can be employed as an addition to surgical synovectomy. Little is known about the effects of this drug on cartilage. This study was designed to investigate the cytotoxic impact of sodium morrhuate on human chondrocytes and cartilage tissue in vitro. Primary chondrocytes from 13 patients were isolated and cultivated in three-dimensional alginate cultures. Furthermore, femoral cartilage explants of 10 patients were cultivated in vitro. Both chondrocytes and cartilage explants were exposed to mixture of sodium morrhuate and mepivacaine in different concentrations simulating chemical synovectomy. After 48 h, cell proliferation, viability, and cytotoxicity were measured. The cartilage specimens were analyzed for apoptosis by immunohistochemistry. Up to a dilution of 1:600, cells were found to be 100 % viable with a proliferation rate of 74 % compared to controls. From 1:400 onwards, a significant increase in LDH release was measured which reached at dilution of 1:200 74 % of high control, whereas histological examination showed no proof of apoptosis or necrosis in cartilage tissue. The results of this in vitro study demonstrate that the cytotoxic effects of sodium morrhuate on human chondrocytes, which lack their original extracellular matrix, manifest between dilutions of 1:500 and 1:400 and increase with higher concentrations of the drug. This effect was not found for cartilage explants, though.

[Prosthesis loosening]. / Prothesenlockerung.

Prosthesis loosening is becoming more and more important due to increasing numbers of primary arthroplasty. Especially in patients suffering from rheumatoid arthritis this is a major topic due to younger age and multiple affected joints. A carefully performed diagnostic regimen is essential for ruling out septic loosening of the prosthesis. Preoperative planning is crucial for revision surgery. Revision implants should be available as back-up. Revision arthroplasty is a technically and economically demanding procedure. Costs for revision surgery are much higher than for primary arthroplasty due to longer hospital stay, intensive care, microbiology, histology, diagnostic imaging, implants and antibiotics. Revision arthroplasty should be performed in highly specialized centers.

[Revision implants of the future: trends and new developments]. / Revisionsimplantate der Zukunft: Trends und neue Entwicklungen.

According to current prognostic studies the numbers of revision operations of hip and knee arthroplasty will increase worldwide. As many patients undergo several revisions and become older at the same time, orthopedic surgeons will have to cope with vast bony defects during operations. The introduction of highly porous metals as surface layer or metal augments has facilitated primary stabilization of prostheses. Short and mid-term results of these new products are promising. New developments in coatings, such as cationic antimicrobial peptides represent new alternatives for antibacterial therapy of periprosthetic infections and increase osteointegration of prosthesis components. Furthermore, the new revision systems have a modular design and can be individually adapted to the patient's bony conditions during operations. In most cases this can be done without cement or in a hybrid technique.

[Patient satisfaction and muscle torque after total knee replacement in dependence on body mass index]. / Patientenzufriedenheit und Muskelkraft nach Knietotalendoprothese in Abhängigkeit vom Body-Mass-Index.

AIM: In a monocentric study, we investigated patient satisfaction, clinical outcome and isokinetic muscle torque in dependence on the body mass index (BMI) in the mid-term outcome after total knee arthroplasty. PATIENTS AND METHODS: A group-matched study with two groups (each 40 knee arthroplasties in 40 patients) with a normal body mass index (BMI 20-25) and above 25 was conducted. The groups were matched for sex, diagnosis and age. Satisfaction, HSS score and isokinetic torque parameters with the Cybex 340 system were measured. RESULTS: There were no differences in the demographic data except for BMI. The HSS score was significantly lower in the overweight group (p = 0.04). Also there were more patients with an HSS score below 60 (bad result) in the group with the higher BMI (0 vs. 9, p = 0.002). Only one patient was not satisfied in the normal weight group, whereas 9 patients in the group BMI > 25 were not satisfied (p = 0.014). No differences between the groups could be found in maximum torque, work and power. CONCLUSION: The patient satisfaction was much lower in patients with BMI higher than 25. There were no differences between the groups in isokinetic torque parameters.

[Repair of local cartilage defects in the patellofemoral joint]. / Therapie lokaler Knorpelschäden im Patellofemoralgelenk.

Cartilage defects of the patellofemoral joint represent different entities. Results of patellofemoral cartilage repair are often variable. Concomitant pathologies, such as malalignment and instability are frequent. Currently no common treatment concept exists. Improvement of patellofemoral biomechanics, e.g. tubercle transfer, results in better outcome independent of the cartilage repair technique used. In patellofemoral instability reconstruction of the medial patellofemoral ligament (MPFL) has recently become a focus of interest. Microfracturing and osteochondral cylinder transfer/mosaicplasty are recommended for smaller defects, while comparative studies have shown advantages for autologous chondrocyte implantation (ACI) in defects larger than 4 cm². In our study patients with patellofemoral scaffold ACI (MACI®), better Lysholm scores were seen with isolated trochlea defects rather than patella defects or bipolar lesions. While trochlea defects can be effectively addressed, treatment of bipolar patellofemoral defects by scaffold ACI cannot generally be recommended. Follow-up treatment of the patellofemoral joint is more time and cost-consuming than other defect localizations. For the development of therapeutic algorithms further well-defined large randomized studies are necessary.

[The 2-year follow-up results of a patient-specific interpositional knee implant]. / Zwei-Jahres-Resultate mit einem patientenspezifischen metallischen Knieinterpositionsimplantat.

BACKGROUND: Besides the primary goal of functional improvement and pain reduction, the operative treatment of unicompartmental arthritis in younger patients is focused on preservation of intact bone and joint structures. The question arises whether an interpositional knee implant based on magnetic resonance imaging (MRI) data can be an alternative treatment option to the established procedures of high tibial osteotomy and unicompartmental knee arthroplasty. METHODS: From June 2004 to May 2008 a total of 33 patients suffering from unicompartmental knee arthritis received a patient-specific interpositional implant (31 medial and 2 lateral) within a single arm trial. The mean follow-up time was 26.6 months (range 1-48 months) and the mean age of the patients was 54.5 years (range 39-65 years). In addition to the clinical results the Western Ontario and McMaster Universities Osteoarthritis index (WOMAC) function scale and the Knee Society scores were measured. A descriptive data analysis, a variance analysis for repeated measurements and a determination of significance level were carried out. RESULTS: The 2-4 year results showed a significant improvement in the WOMAC function scale as well as the Knee Society scores. The knee function after 2 years was comparable to the preoperative situation with an extension to flexion of 0/2/130°. The dislocation rate was 6% and the overall revision rate 21%. CONCLUSION: Despite acceptable functional results a significant pain relief, a complete preservation of bone and a lower rate of dislocations compared to the off-the-shelf Unispacer implant there were only limited indications for the customized interpositional knee implant with respect to the given contraindications due to the high 2 year revision rate.

Biomechanical forces exert anabolic effects on osteoblasts by activation of SMAD 1/5/8 through type 1 BMP receptor.

Osteoblasts are mechanosensitive cells, which respond to biomechanical stimuli to regulate the bone structure through anabolic and catabolic gene regulation. To examine the effects of mechanical forces on the osteogenic responses through the SMAD signaling in osteoblasts, the cells were cultured in well-characterized mechanoresponsive 3-D scaffolds and exposed to 10% dynamic compressive strain (Cmp) at 1 Hz. Subsequently, SMAD phosphorylation and osteogenic gene induction was examined. Osteoblasts cultured in 3-D scaffolds exhibited increased constitutive SMAD 1/5/8 phosphorylation, as compared to monolayers cultures. This SMAD 1/5/8 phosphorylation was further upregulated after 10, 30 and 60 min in response to Cmp, exhibiting a peak activation at 30 min. No significant changes in SMAD2 phosphorylation were observed, suggesting signals generated by Cmp may not activate the Transforming Growth Factor-ß signaling cascade. Subsequently, biomechanical stimulation-induced SMAD 1/5/8 phosphorylation upregulated the expression of osteogenic genes such as Osteoprotegrin, Msx2 and Runx2. Dorsomorphin, a selective inhibitor of the bone morphogenetic protein (BMP) receptor type 1 (BMPR1), blocked Cmp-induced SMAD 1/5/8 phosphorylation, as well as Osteoprotegrin, Msx2 and Runx2 gene expression. Collectively, the present findings demonstrate that biomechanical stimulation of osteoblasts activates SMAD 1/5/8 in the BMP signaling pathway through BMPR1 and may enhance osteogenesis by upregulating SMAD-dependent osteogenic genes.

[Histological pathological investigations and arthroplasty: do they make sense?]. / Histologisch-pathologische Untersuchung bei Gelenkersatzoperationen: Sinnvoll oder nicht?

The present article discusses for which arthroplastic operations a histology investigation should be performed and in which cases histological analyses can be omitted.

[Importance of computer-assisted navigation in total knee arthroplasty - results of a nationwide survey in Germany]. / Aktueller Stellenwert der Navigation in der Knieendoprothetik in orthopädischen und unfallchirurgischen Kliniken in Deutschland.

AIM: Total knee arthroplasty is one of the standard procedures in severe osteoarthritis of the knee. Computer-assisted navigation systems became more popular in the last decade. Navigation systems improve the component positioning and the alignment in total knee arthroplasties. The aim of this survey was to capture the actual trend in computer-assisted total knee arthroplasties in Germany and to discuss the results in comparison to the current literature. METHODS: A questionnaire form was sent to 506 orthopaedic and trauma surgery departments in Germany. The first part of the survey included general questions about the department and total knee arthroplasties. The surgeons were asked about their application behaviour and their rating of computer-assisted navigation in total knee arthroplasty in the second part. Questions concerning total knee arthroplasties, unicondylar knee arthroplasties and revision total knee arthroplasties were included in the form. RESULTS: 194 of the departments returned the questionnaire. A total of 39 941 knee arthroplasty surgeries were performed in these departments. 35 624 of these surgeries were primary knee arthroplasties including 32 789 total knee arthroplasties and 2835 unicondylar knee arthroplasties. In addition, 4317 revision total knee arthroplasties were performed by the respondents. 60 % of the departments used a computer-assisted navigation system. In synopsis 29 % of the primary total knee arthroplasties, 4 % of the unicondylar knee arthroplasties and 7 % of the revision knee arthroplasties were performed with a computer-assisted navigation system. Minimal invasive surgery was performed in 31 % of the departments and 36 % of these surgeries were done with navigation-assistance. The "ligament-balanced" procedure was the most common used technique to determine the femur rotation in navigated total knee arthroplasties. In 75 % of navigated total knee arthroplasties cemented components were implanted. Overall 65 % of respondents approved of navigation-assisted surgeries and 77 % saw an improved precision by this technique. The number of computer-assisted navigation uses in surgeries is increasing in 34 % of the departments and decreasing in 13 %. CONCLUSION: The computer-assisted navigation in total knee arthroplasties is a frequently used technique. The most respondents support the application of navigation-assisted knee arthroplasties and indicate an improved outcome measured by the postoperative alignment. Nevertheless, long-term results are needed for a final evaluation of navigation-assisted surgery.

[Operative treatment of the unicompartmental knee arthritis - results of a nationwide survey in 2008]. / Operative Therapie der unikompartimentellen Gonarthrose - Resultate einer bundesweiten Umfrage für das Jahr 2008.

BACKGROUND: Despite good long-term results of primary total knee arthroplasty, it is a commonly accepted aim to stave off joint replacement as long as possible, particularly in younger patients. In this situation the surgeon has to make a careful decision whether an arthroscopic procedure will be promising, a corrective osteotomy may be sensible or a joint replacement due to the patient's age is acceptable. High tibial osteotomy had become increasingly popular by use of the opened wedge technique combined with locking compression plates fixation in the past decades while it has been replaced step by step by total knee arthroplasty. In spite of this fact the German national agency of quality management (BQS) showed that the number of total knee replacements in Germany increased from 90 000 in 2003 to 146 000 in 2008. The share of unicompartmental knee replacements in this period doubled from 5.3 % to almost 10 %. The aim of the present study was to inquire current data regarding particular surgical treatment concepts of unicompartmental knee arthritis in Germany. MATERIAL AND METHODS: In a nationwide anonymous survey in May 2009 220 departments of orthopaedics and 230 departments of trauma surgery were asked about their treatment strategies in unicompartmental knee arthritis in middle-aged patients (30 to 60 years) with unilateral Outerbridge grade III-IV lesions. Overall 46 questions in 6 subject areas (structure of the department, number of treated patients, surgical methods, anaesthesiological procedures, perioperative management, postoperative treatment) were posed. With regard to the item "operative treatment" we asked for the importance of arthroscopic procedures, corrective osteotomies and different procedures of joint replacement. The interpretation was done with invariant data analysis by indication of numerical frequency and percentage distribution of selected options. RESULTS: Questionnaires were returned by 51.1 % of the surveyed departments. This represents a total number of 76,028 procedures in unicompartmental knee arthritis in middle-aged patients. First of all, arthroscopic procedures were applied (50.4 %), followed by knee replacements (43.4 %, of which 87.3 % were total knee replacements, 12.3 % unicompartmental knee replacements and 0.4 % tibial hemiarthroplasties) and corrective osteotomies (6.1 %). In 59.8 % of the 38,376 arthroscopic procedures a microfracturing and in 28.2 % an abrasion arthroplasty was done. Most of the corrective osteotomies were performed at the proximal tibia (90.9 %) using an open wedge technique (73 %) and internal fixation with locking compression plates (72 %). 75.2 % of the responders performed cemented unicompartmental arthroplasties (97.8 %) with an average number of 23.2 per year. 43.4 % believe that bicompartmental arthroplasty in case of additional affection of the femoropatellar joint is an option and 22.6 % believe in the expected advantages of patient-specific unicompartmental implants. Total knee arthroplasties are performed with an average of 197.4 per year, most frequently using the free-hand technique (85.5 %) and medial-parapatellar approach (82 %). Interpositional knee devices were only used in 9.1 % of responding departments with an average number of 6.6 per year. Only procedures with low difficulty level such as arthroscopies were done by residents in a higher number (16.9 %). Procedures with higher difficulty level were mainly done by consultants, senior or chief surgeons. CONCLUSION: In total, arthroscopic procedures still play an essential role in the treatment of unicompartmental knee arthritis prior to joint replacement. Total knee arthroplasty was preferred even though the number of unicompartmental knee replacements was only slightly increasing. Periarticular corrective osteotomies have gained in importance since the introduction of locking compression plates. Interpositional knee devices play a minor role in the treatment of unilateral knee arthritis in Germany.

Fatigue fracture of the hinge pin in a semi-constrained total knee arthroplasty: a case report.

Material failure is a rare complication in total knee arthroplasty (TKA). This case report shows a fatigue fracture of the hinge pin as a consequence of a postoperative persisting valgus deviation in a semi-constrained TKA.